As the city slopes towards the lake, it splits into two strata and this subterranean world appears. the streets become double-layered with the service functions underground and the more public-functions above. it's actually a really clever way to segregate the two types of functions and it removes the heavy trucks, service and garage doors, and waste facilities from view and makes the upper level (somewhat) more pedestrian-friendly. this is the entrance near Michigan Avenue and Illinois Street.