An awesome, and sometimes free, ferry that links Manhattan at the Financial District to Ikea in Brooklyn via Red Hook. Very great views of the city and if you end up having to pay it's redeemable for a monetary discount towards an Ikea purchase. I think of it as a treat and an investment.
Having the experience of owning and running a coral reef aquarium (and frequenting this particular shop about once a week) - I was sad to hear it closed it's doors. Their reef display tank was always amazing. These pictures were taken from PetCo at Union Square (I also used to go there for my saltwater needs).
The New York Earth Room is an interior sculpture by the artist Walter de Maria that has been installed in a loft at 141 Wooster Street since 1977. Go see!
A living archive preserving history and promoting scholarship of grassroots urban space activism by researching and archiving efforts to create community spaces. They also exhibit materials that document these actions, to educate people on the political implications of reclaimed space.