Grab drinks on top of the Ren Cen. Or at Cliff Bells, or the Park Bar. If you want to stun them with architecture, take them to the lobby of the Guardian Building [[not sure what time the lobby closes). Also the lobby of the Compuware building is pretty neat. If the weather is cooperating, then try walking the riverwalk from Hart Plaza heading east towards the bridge to Belle Isle. Punch Bowl Social is opening in about a month unfortunately, but it sounds like it'd be a fun place to hang out.