Agios Sostis: Marathonissi, Keri Caves, and Turtle Spotting

The real draw here is the chance to see Caretta Caretta turtles in the protected waters off Zakynthos, then swim in clear water near the Keri Caves. The glass-bottom boat gives you something to watch even when you stay dry.

I like the friendly, capable captains and the good mix of wildlife, scenery, and swimming. I also like the price: at $29 for three hours, this is a fairly easy way to sample the marine park. The main caution is that turtle sightings are never guaranteed, and several boats may gather around one animal.

Key points to know before booking

• Turtle spotting comes first: The boat looks for loggerhead turtles in their natural setting, but sightings depend on luck and conditions.
• Oasi Bay provides the swim stop: You can swim and snorkel near the Keri Caves area, but you cannot swim inside the cave.
• Marathonisi is protected: Only a small part of its beach is open because it is a turtle nesting ground.
• The glass bottom adds interest: You can watch the water below while seated in the shaded area or on the rear sundeck.
• Three hours keeps the outing manageable: You get turtles, caves, a swim, and island time without giving up a full day.
• Bring your own basics: Sunscreen, a hat, sunglasses, towel, swimwear, food, drinks, and snorkeling gear are all useful.

A $29 boat trip into Zakynthos National Marine Park

This short cruise from Agios Sostis is built around three simple pleasures: looking for turtles, swimming in clear water, and seeing Zakynthos from the sea. At $29 per person, it is priced as an accessible half-day outing rather than a luxury cruise.

I think the value is strongest if you want several experiences in one ticket. You get a glass-bottom boat ride, a stop near the Keri Caves, a visit to Marathonisi, and time for swimming. Food and drinks are extra, and hotel pickup is not included, so your true cost will be slightly higher if you need to arrange transport or buy refreshments.

The boat has a shaded seating area and a rear sundeck. That matters on a bright Greek afternoon. You can sit out in the sun for the views, then move under cover when the heat becomes too much. Large bags and luggage are not allowed, so arrive with a small beach bag rather than a suitcase.

The meeting point is easy to identify: look for the Nautilos flag directly in front of the boat at Agios Sostis harbor. The captain welcomes you there. The available languages are Greek and English, and several recent outings were praised for friendly, accommodating captains who could communicate well with mixed-language groups.

Leaving Agios Sostis with the marine park ahead

Once you leave the harbor, the outing becomes less about getting somewhere and more about watching the water and coast change around you. The boat heads into the protected waters of the National Marine Park of Zakynthos, an important breeding area for loggerhead turtles.

The glass-bottom section gives you a chance to look below the surface as the boat moves. It will not replace snorkeling, but it adds a useful second view of the sea. You can keep an eye out for movement below while the captain points out sights around the island.

The rear sundeck is the place for open views and a breeze. The shaded section is better if you have young children, want to stay out of the strongest sun, or simply prefer a cooler ride. Bring a hat that fits securely, since the boat is open to wind.

The atmosphere depends partly on the group and partly on the captain. The strongest feedback centers on captains who were funny, welcoming, and willing to help. One outing included a small departure delay, but the group received notice in advance and the captain worked to accommodate everyone. That is useful to know if you have a tight schedule afterward: allow a little flexibility rather than planning an immediate connection.

Looking for loggerhead turtles in protected waters

Turtle spotting is the emotional center of the trip. Caretta Caretta loggerheads use the beaches around Marathonisi and the wider marine park for breeding. Seeing one in the water, rather than in an aquarium or rescue center, can be a memorable moment.

Still, keep your expectations sensible. A sighting is possible, not promised. One July outing had several turtle sightings, while another group saw a single turtle. Seasonal timing can matter too. By July, some turtles may have moved away as their eggs hatch, so an early or later visit may not produce the same result.

You should also understand the practical side of wildlife watching. Boats can gather around a turtle, and that can feel uncomfortable if several vessels are trying to follow one animal. Give the captain room to make responsible choices, and do not expect a private wildlife encounter. The turtle is the priority, not the photograph.

The best approach is to enjoy the whole route rather than judge the trip only by the turtle count. The views, swim stop, glass-bottom boat, and Marathonisi visit still make up most of the three-hour experience. If you see a turtle, treat it as a wonderful bonus.

Swimming near Oasi Bay and the Keri Caves

The boat usually stops at Oasi Bay, close to the Keri Caves area. This is your chance to get into the water, cool off, and use snorkeling gear if you bring it.

The sea near the caves is the sort of setting that makes the stop worthwhile even for people who are not keen snorkelers. Blue light plays across the pale limestone, and the water provides a striking contrast with the rock. You can swim near the cave area and take photographs from the boat, but you cannot swim inside the cave itself.

That distinction is important. The promotional wording may make the caves sound like a place to enter, but the actual activity includes swimming in the surrounding area, not inside the cave. The captain will choose the exact stop based on the conditions and the route.

Bring water shoes if you have them, since one person cut a foot after slipping on a rock. That incident was handled helpfully by the boat driver, but it is a good reminder to take care when climbing in or out of the sea. Rocks can be slippery, and excitement can make people move too quickly.

This stop is also the best part of the tour for a proper swim. The Marathonisi beach visit is more about sitting, walking a little, and seeing the nesting area. If swimming is your main reason for booking, pack your towel and swimsuit where you can reach them quickly.

Marathonisi, the Turtle Island beach stop

Marathonisi, often called Turtle Island, comes next. As you approach, you see pine, olive, and green oak growth covering the island. From the water, the island feels much more natural than a developed resort beach.

The beach is protected because loggerhead turtles lay their eggs there. Only a small portion is open to people, so do not expect to wander along the entire shore. The restriction is part of the point of the visit. You are seeing a protected nesting area, not arriving at an ordinary beach club.

You get free time on the island. You can swim, sit in the shade, take photographs, or buy a snack, drink, or ice cream at the bar. Food and drinks are not included, so bring your own supplies if you want to avoid spending extra, although the bar gives you an easy option.

The stop is roughly an hour according to the timing described by one participant, but exact time can vary. That is enough for a relaxed break, yet not enough for a full island outing. Plan on a compact visit rather than a long beach afternoon.

I would keep expectations moderate about the beach itself. One person found it fairly ordinary and thought the tour might improve with a different stop. The attraction is not a wide range of facilities or a remarkable beach experience. It is the combination of protected turtle habitat, island scenery, and a pause on shore.

Shade is available, which is helpful in the strong summer sun. Still, wear sunscreen and carry water. The open beach area is limited, and the surface may not suit anyone looking for a fully organized, accessible resort setup.

What the three-hour schedule feels like

Three hours is a smart length for this particular outing. You get enough time for a boat ride, wildlife watching, a sea stop, and Marathonisi without committing an entire day.

The pace is active but not rushed. You will spend part of the trip seated and watching the coast, then switch to swimming and shore time. The main limitation is that every stop must fit into a short window. If the turtle search takes longer, or if departure runs late, time on the island may feel brief.

This works well for a family with children who may lose patience on a longer cruise. One parent described a child loving the turtle sighting, and the swim stop provides a clear break from sitting. It also suits couples and small groups who want a scenic water outing without paying for a full-day charter.

It is less suitable if you want quiet, private wildlife viewing or a long, secluded beach visit. You are joining a shared boat, and the route may attract other boats in the same area. The reward is the low price and the variety.

What to bring for a more comfortable trip

Pack as if you are spending a few hours at the beach, not taking a formal sightseeing cruise. The essentials are:

• Swimsuit and towel
• Sunscreen and a sun hat
• Sunglasses
• Water and snacks
• Snorkeling gear if you have your own
• A small bag rather than luggage

Food and drinks can be purchased on Marathonisi, but they are not included. Bringing your own water is sensible, especially if you do not want to wait until the island stop.

A waterproof phone case is also practical for the swim and turtle photographs, though this is general beach advice rather than a supplied feature of the tour. Keep your belongings compact because large bags are not permitted.

Use care around the rocks at the swim stop. The boat driver can assist if something goes wrong, but prevention is better. Move slowly, watch your footing, and do not assume the entry point will feel like a paved beach.

Who will get the most from this boat trip

I would recommend this outing to you if you want a low-cost introduction to the marine park and prefer variety over a single long stop. It gives you wildlife, caves, swimming, an island, and sea views in one short outing.

Families can benefit from the compact schedule and the chance to see turtles. Children may also enjoy the glass-bottom view, especially if they are not confident swimmers. The shaded seating area helps, though you still need to manage sun exposure.

It also suits first-time visitors to Zakynthos who want to see the coast from the water without arranging a private boat. The English and Greek-speaking captain can explain the route and help with the practical parts of boarding and swimming.

You may want a different experience if your main goal is serious snorkeling, a quiet beach, or an in-depth cave visit. The boat only stops near the Keri Caves, and the caves themselves are not open for swimming inside. Marathonisi is protected and limited, not a large beach destination.

Booking details that affect your decision

The meeting point is at Agios Sostis harbor, in front of the boat with the Nautilos flag. Hotel pickup and drop-off are not included, so you need to make your own way there.

The tour runs for three hours, with departure times dependent on availability. The provider offers free cancellation up to 24 hours ahead for a full refund, and you can reserve now and pay later. Those terms help if your Zakynthos plans depend on weather or changing schedules.

The overall rating is 4.3 from 401 reviews, which fits the experience well: the trip delivers what it promises, but it is not a private cruise and it cannot control turtle sightings, sea conditions, or the behavior of other boats.

Should you book the Agios Sostis boat tour?

Book it if you want a good-value, three-hour introduction to Zakynthos by sea. The friendly captains, clear swimming water, turtle habitat, glass-bottom boat, and Marathonisi stop give you a lot for $29.

Go in with realistic expectations. You may see turtles, but you may also spend time watching several boats search for one. You will swim near the Keri Caves, not inside them. Marathonisi offers a protected beach stop, not a long, fully developed beach day.

For most people staying near Laganas or Agios Sostis, I think the combination is worth the price. Bring sunscreen, water, a towel, and modest expectations about the beach, and you will be set up for a pleasant morning or afternoon on the water.

FAQ

Where does the boat tour meet?

Meet at Agios Sostis harbor in Laganas. Look for the Nautilos flag in front of the boat, where the captain will welcome you.

How long does the tour last?

The tour lasts three hours.

What is included in the price?

The price includes the glass-bottom boat ticket, the visit to Marathonisi, a swim stop, and the Keri Caves and Oasi Bay area.

Are food and drinks included?

No. You can buy snacks, drinks, and ice cream at the bar on Marathonisi, or bring your own food and drinks.

Can I swim inside the Keri Caves?

No. You can swim near the Keri Caves area, but swimming inside the cave is not allowed.

Will I definitely see a turtle?

No. The tour looks for loggerhead turtles in their natural habitat, but sightings are not guaranteed.

How much of Marathonisi beach can I visit?

Only a small portion of the beach is accessible because the beach is protected as a turtle breeding ground.

Is the boat shaded?

Yes. The boat has a shaded seating area as well as a rear sundeck.

What languages are available?

The host or greeter speaks Greek and English.

What should I bring?

Bring sunglasses, a sun hat, swimwear, a towel, sunscreen, food and drinks, and snorkeling gear. Large bags and luggage are not allowed.