The Hotel Congress is a 1919 railroad hotel across the street from the Amtrak station, and the centre of Tucson nightlife for nearly a century. The downstairs Tap Room and Cup Café have been continuously open since the 1930s; the Club Congress dance floor next door does live music most nights.
The hotel's rooms are simple and old-school — no televisions, working steam radiators, original transom windows. Spend an hour even if you are not staying: have a drink at the Tap Room, look at the FBI files on display from the Dillinger arrest, and walk the Congress Street strip on either side.