Barcelona Aquarium is also a must see especially if you have kids, it's location at the end of Las Ramblas at the end of the pier is easy to find. Look out for the Mediterranean exhibit totalling an impressive 14 tanks that represent various aspects of the ocean in this area and take a stroll through the methacryllate tunnel of the Oceanarium where it feels as if you are at the bottom of the ocean swimming with the sharks. Explora! is a great exhibit for the younger ones as it's very interactive with lots of buttons and knobs to touch, videos to look at and listen to, and nature to investigate and discover.