Carleton university in Ottawa has something like 5km of tunnels connecting every building on campus. What can I say, Canadians have oddly dwarven compulsions to dig underground complexes?

The university of Minnesota has a lot of tunnels. they were put into place because there is a central steam place and maintenance needs to inspect those pipes, but they are also open to anyone to use (or were when I went there year ago). When it was very cold it was nice to be able to get around - but often the tunnels were not very direct so I didn't use them much.