This is a nice little island crag that offers some nice moderate climbing away from the crowds and lookey-lous typically encountered at Diablo. The rock is good and offers both sun and shade for whatever season you are there. There are great views from on top of the island. Some guide books have referred to this as the Alcove. The crux used to be getting off of the island, which is no longer required.
Getting There
Same approach as for The Grotto but continue up The Grotto on a talus field and veer to the west at The Grotto's exit. Continue to the top of this little mesa which is the top of The Grotto's West Wall. Then scramble across and down into another talus gully where the east facing side of Gilligan's Island can be viewed.
The Classics
Mountain Project's determination of some of the classic, most popular, highest rated routes for Gilligan's Island (AKA: The Alcove):
Generally two groups developed climbs at Diablo in the 1990s. This explains the double naming pattern. The person who publishes first seems to establish the name.