Can a student/tourist visit your Chicago company (37signals et al)?

Hey guys,<p>I am visting the US, Chicago to be specific, this coming week as part of a program. I am about to graduate and I would love it if I can get to visit some startups or companies in the area. I am fan of several of them such as Braintree and 37signals, so I would appreciate any directions leading me to similar places.<p>Thanks!