This is definitely worth the money and an excellent way to do something different and see the sites. We booked on for one of the cruises that left around 11am and returned about 2pm.
You queue and board the boat in the harbour on the livelier side of San Antonio. This is also where you can buy tickets if you have not already purchased them or grab something to eat or drink you board.
Once everyone is aboard, the boat sets off and the Captain gives some commentary over the different sites to see as and when you approach them. When you board, you are given plastic glasses (one per person) which you keep with you and you use to get drinks from the bar on the first floor deck.
The boat consists of three decks, a glass bottom deck, the middle deck where the bar, indoor seating and a toilet is located; and then the open air main deck where the bridge is (where the Captain navigates from). We chose to sit on the top deck in a slightly covered area to avoid the heat.
The boat sets off and the music starts and the first main stop is the aquarium which is built into the side of a mountain and forms a cove. Entry fee is included in your ticket. You have about fifteen minutes to have a look around and there is a bar there where you can buy food and drink.
The captain sounds the horn when the boat is ready to go and you set sail.
The captain makes an announcement when the bar is open and you make your way to the bar to choose from a selection of cold drinks including beer and soft drinks. The beer is really refreshing when it is so hot as is the free fruit and snacks that are provided after when you have had a swim.
You navigate around a couple of sites before the captain stops the boat and you can jump off the back or the front of the boat. Floats, goggles, etc are provided free of charge and you have about 45 minutes to swim.
Once aboard, fruit is available next to the bar.
You then make your way to drop off at Cala Salada before turning around and making your way back to Ibiza Harbour.
Overall, it is a great way to spend an afternoon and more than worth the money.