Travel agencies advertise day trips to Kekova as the prime attraction near Kas. Personally, I found the trip hugely disappointing and would not recommend it.
There are two ways to visit the Sunken City at Kekova, a collection of somewhat interesting Lycian Ruins that have slid the sea’s surface. The first is on a tour boat, although there’s quite a bit of variety in terms of price and itinerary. If possible, try to go on a glass-bottomed boat that will give you a better view of the Sunken City as you pass over it (you’re not allowed to stop). Also, if you’re prone to seasickness, you may wish to take a tour that drives to Ucagiz and then sets off by boat from there, as this itinerary cuts a significant amount of relatively uninteresting water travel from the journey.
The second, and in my view, more interesting way to visit is by sea kayak. It’s a bit more expensive (60 TL at most agencies vs. 30 to 50 for the boat) and more active, but it also gets you much closer to the water. I went with Xanthos Tours/, who were very helpful to me as a first time kayaker. However, they did push the tour to go faster than necessary (with the result that we arrived earlier than planned) which reduced my enjoyment of the experience. Also, it’s worth noting that it’s easiest to kayak in a tandem than alone, so you’ll be better off if you’re traveling with a friend or there are an even number of people in your tour. I was kayaking alone (everyone else on the tour was traveling in a couple). These caveats aside, I’d recommend seakayaking as the best way to see Kekova, although frankly I can’t recommend the trip in good conscience.
Kayaks and boats alike take you first to a swimming spot near some Byzantine ruins on Kekova Island, which lies just offshore from the somewhat ramshackle town of Ucagiz (you could stay here rather than Kas but you’ll pay more for less satisfactory accommodation). After a half hour or so here, you pass by the ruins and it’s here that a kayak is most advantageous as it allows you to pass much closer to the shoreline (where the ruins are located) and also much closer to the underwater ruins themselves since you’re just above the waterline. You’re not strictly allowed to stop at the ruins themselves (nor are you allowed to snorkel or dive to them), ostensibly to prevent damaging them although this seems slightly excessive in this case, and if you’re lucky you’re treated the spectacle of seeing some underwater pots, stairs, house walls, and rubble.
Afterwards, you stop for a very small-proportioned lunch at the village of Kale, overlooked by the Byzantine castle of Simena, which is a popular yacht harbor. It’s possible to climb to the castle on the lunch break, although it’s not worth spending the 12 TL entry fee (even according to the travel agency!) After lunch, if you’re kayaking you pass by a submerged Lycian necropolis, which includes the evocative sight (included on virtually every advertisement for the trip) of a sarcophagus perched just over the waterline. If you’re taking a boat, however, you just head straight back to Ucagiz (if you drove to the area) or Kaş (if you came directly by boat). As should be evident from my review, the trip is something of a disappointment, especially given the enthusiasm with which it’s advertised in Kaş, and while my introduction to sea-kayaking was enjoyable, the trip itself was hugely disappointing.