As a student on campus at Barnard, you'll be able to take advantage of all the facilities that the Barnard and Columbia University systems have to offer. However, you'll find that as a Barnard student living on the west side of Broadway, Barnard's facilities are much more convenient to use. The one exception to this rule is the Dodge Fitness Center, which is Columbia's gym. If you want to work out, then you won't mind walking across the street to Dodge, which is a much better gym than LeFrak, the gym Barnard has to offer. No one really uses LeFrak, except for events such as Midnight Breakfast and for Barnard PE classes, while Dodge offers lots of exercise equipment both in kind and quantity.
Most of Barnard's facilities aren't great, and most go unused. Most students don't care too much, though, because, as part of Columbia University, they have access to everything on any campus. Whatever kind of facility you're looking to use, it's out there. It might just be a little farther away than you'd like. What really makes Barnard's facilities great, though, are the people that work in each one to make sure that the students are well taken care of, which is something you don't find at too many schools.