Lewiston (37,000) will remind you of a smaller version of Lawrence, MA and Auburn (24,000) will remind you of nothing in particular. You'll come away from your visit realizing the that "Twin Cities" are not similar to each other in either size or appearance. Lisbon Street is the main drag in downtown Lewiston and is an interesting stroll and has the third most "urban" vibe in the state after Congress and Commercial Streets in Portland. Auburn has benefited more than it's bigger city across the river when it comes to new developments post 1975 with a few mid rise commercial buildings and a hotel in Great Falls Plaza. Both cities have come a long way in sprucing up their commercial cores and are worth a day trip to explore and don't forget to check out Bates College and the Basilica in Lewiston for its impressive architecture.
DZH22, would you mind adding this photo to the "Lewiston, Maine's second largest city" thread to inject some life into it?