There are several tour agents offering boat trips and snorkeling to Kicker rock, Isla Lobos or other visitor sites. You can rent equipment to hike, camp, bike, or snorkel at many of these places. It's also possible to do scuba diving. There are three scuba shops on the island; GalaKiwi, Chalo Tours, and Galapagos Expeditions. GalaKiwi is better for experienced divers, the guide tends to swim fast and not point out too many things. Chalo Tours speaks English, Spanish, Danish, and German. They have reasonable prices and all the guides are great. The main guide for Galapagos Expeditions is trained by Chalo Tour's main guide.
Renting a mountain bike is also possible and cost around $10 per day. Most bikes are not mountain but are sufficient for around town and on the roads up to El Progreso the other town on the island.
A taxi pick-up truck can be rented to drive to Puerto Chino, one of the best beaches on the island. It will cost between $40-50, but you can always grab a crowd and split the price. This is a gorgeous beach with soft white sand and is the furthest point into the island that one can go without naturalist guide.
While you're in the highlands, you may want to stop by the Galapaguera to see the breeding center of the San Cristobal variety of tortoises, which is right near Puerto Chino. El Junco, the only large freshwater lake in the Galapagos, is also a popular site.
There are several excellent places to surf around the island as well. During off season there are frequently waves at Punta Carrola and Tonga Reef. As the season picks up, El Canyon and a few other places have "buenas olas". Check with the locals about where the waves are daily and to ask for directions. IF there are waves, someone is almost guaranteed to be going surfing and most will invite you to follow them!
