I think we just repurpose storm drains for that. Always bring a ladder with you in the trunk of the car!

(I'm kidding. Chicago has a mildly extensive two level street system, and there are just doors in the "basements" of buildings that open up to the subterranean streets. I always thought it was neat, but was also afraid to walk around on the lower level. Also, the top level wasn't parks, it was just more car lanes.)