We did a Kekova sunken city boat trip and it was a great experience. The water color is just insane!!! There were 4 swimming stops and 1 stop in the village where you could leave the boat and go for a stroll.
The price is about $50 per person and includes a very good lunch. I booked a day in advance and they still had spots. The crew is very nice and the captain is taking drone videos for the passengers for free.
When you pick up your tickets, try asking for the ‘VIP’ seating - it’s a spot on the front of the boat where there is both shade and sun.