Until the mid 1980's, Gorgona Island was Colombia's Alcatraz style high security prison. The prison is now derelict, complete with swinging monkeys and a range of other animal and plant life, and makes for a fascinating visit. Gorgona Island also has a few unspoilt sandy beaches, and the area is great for nature tours, birdwatching and snorkelling. The whole travel experience is like none other. Gorgona Island is also Colombia's best spot for whale watching - the best months are from July to September, when killer whales, amongst others, are often seen.
In terms of visiting Isla Gorgona, you're best off contacting Aviatur, who manage all of Colombia's National Parks. They'll book an all inclusive package that includes flights to nearby Guapi, a two hour boat transfer plus the islands accommodation (there's one place to stay) and food. The package is not for those on a tight budget - it might be a little cheaper if you get to the island yourself (a gruelling 12 hour boat trip from Buenaventura, arranged locally).