Zakynthos

The day here is a short boat run. Turtle Beach Diving Center sits directly on the beach at Limni Keriou and operates three boats, Euro Divers works from Laganas Beach, and three further PADI shops are based around the island. Boat time to most of the Keri sites is under 30 minutes, and Marathonisi is about 15 minutes out, so two-tank mornings are the pattern rather than long crossings. Centres ask for a certification card, a logbook and proof of dive fitness at check-in and start guests with a check dive. Trips run May to October.

The terrain is limestone: caverns, walls and rock reefs in a band that mostly sits between 5 and 30 m. Keri Caves runs through a 75 m cavern open to the sky, entered around 12 m and finishing at 5 m; Marathia and Marathonisi are easy 10 to 21 m reef dives with no current. The Arch and Elephant Reef are the other end of the scale — per-dive averages stay near 18 m, but the walls behind them drop to 70 and 75 m, and The Arch carries current to two knots, so depth discipline matters there. Nudibranchs, triton shells and octopus turn up under the boat at Marathonisi, a jackfish school works the back of its rock, and the caverns are where the monk seal appears.

It suits divers of most levels: the operators grade two of the Keri caves for everyone and keep one for the genuinely experienced, and The Arch itself is rated from Open Water even though its wall keeps going. Marathonisi sits inside the National Marine Park of Zakynthos, where fishing is banned in every zone and boats are kept off the nesting beaches. Night dives run as an add-on from Limni Keriou, but divers after wrecks will not find one on the roster, and the open reefs carry the Greek problem of overfished water, so this is a place for rock, caverns and the chance of a seal rather than dense fish life.