An adventure tour to Tortuga Island is very popular for visitors to the Nicoya Peninsula. I will explain the offerings of the tour and then talk more about our own experience.
Tour Schedule
Take a boat out to Tortuga Island - approximately 1 hour.
Snorkel from the boat.
Land on the island and have lunch (fish, chicken, or veggie).
On the island, suntan, play volleyball, or pay additional money for the on-island zipline tour. Spend about 4 hours.
Our experience
We went with a small tour operator in Montezuma, one of the several. Since Montezuma has no dock, you board a speedboat by wading into the water and climbing quickly into the boat. A very bumpy ride followed the shoreline. The tour guide told us about some of the sights we passed, including a waterfall pouring into the ocean, a hole carved by waves into a rock, and a famous beach resort. Once we arrived at our destination, we all put on snorkeling equipment.
The cloudy weather made snorkeling prospects dim, but the water was very warm for swimming. Unfortunately, my partner had a mishap. When getting back in the boat, she tripped and fell, breaking the guide's sunglasses. He was quite angry about the sunglasses, but not concerned for her wellbeing. Her foot swelled up and was painful to walk on for 2 days thereafter.
On the island, we discovered that it wasn't uninhabited at all. In fact, it has its own gift shop, although no bathrooms. This lack of bathrooms is inconvenient. Lunch was delicious - lots of fresh fruit and barbequed fish. The rest of the day was free for exploring a very small strip of beach. It was beautiful, but not worthy of an afternoon. Some people played volleyball. My partner was too hurt to even wander around. Swimming was not possible due to the coral reef that started not too far into the water. The most exciting part of the day was figuring out how to pee with no privacy. One had to wade into the water and sit down, since the interior of the island was closed off to visitors. We were very bored and couldn't figure out why everyone said visiting this "deserted" island was such a great idea.
On the way back, the driver made sure to keep bumping the waves in such a way to cause us all to have enormous butt bruises. When exiting the boat, it rocked and my partner's hurt foot was thrown onto the propeller. She limped away. Then the guide demanded $20 for his sunglasses.
Overall, we did not enjoy ourselves.
In summary, if you want a luxury trip, go with Calypso Tours, which I've heard good things about.
Watch out for sunburn.