I was sorely tempted to place this in the tourist traps section, as I don't believe the aquarium is good enough to justify the 2000 yen entry price.
That said, it is interesting enough, and it does showcase the diversity of Sagami bay.
The exhibits themselves are generally pretty good, and there is English language signage in a lot of different areas.
If you are in Kamakura then you may want to visit Enoshima Island for a half day trip. Or you may want to visit Enoshima Island for a full day trip.
Taking the tram(Enoden line) to Enoshima station is an experience itself. The tram passed through a very narrow street which has houses that were a few inches away on either side of the street.
Enoshima is a small island and its perimeter is approximately 4km and can be easily explored on foot. You can walk across to the Enoshima Island by the Enoshima Benten Bridge or you can take a short boat ride(5min) across to the far end of the island(near Enoshima Iwaya Cave). The fare(one way) for adult is 400yen and for children is 200yen. There are many sovenier shops and eating places on the island.
Places of interest are: 1)Hadaka-Benten, or the naked goddess of entertainment in the shrine, 2)Tropical Botanical Garden 3) Enoshima Lighthouse 4) a cave(Enoshima Iwaya) which is created by many years of sea errosion. Inside the cave, there are stone statues of Buddha and some mysterious stones that glow inside the cave. 5) Ryuren no Kane(the bell of Dragon's Love) etc.
A good place to combine with a trip to Kamakura, Enoshima island is a very nice, if tourist-packed place to visit. Avoid coming here during pea season, as the paths through the temples etc are very narrow at times.
I would also recommend that you spend longer here, as there are some areas that most people don't tend to visit, allowing some peace and quiet to remain.
The Sea Candle is an observation tower up on the hill on Enoshima. It gives a panoramic view of the overall area. 300 yen entry.
Enoshima island has an amusement park, botanical garden and observation tower which was renovated recently.
The island used to be part of the main island but erosion separated it !
To go to the top of the island, you have to follow a curvy street lined up with stores and restaurants. You won't regret the walk, it's wonderful once on top !
You can now take elevator on top of the tower. The view from the top is magnificent. See my travelogue for more pictures.