I'd second that suggestion to take the CAT Shuttle.

You can take a 1 1/2 hr tour with Grayline or one of the other trolley companies then take the free shuttle back to where you want to spend some time.

It costs about $14 for the round trip tour and $21 for the tour you get on and off at will. The Cat Shuttle is free and you can get on and off at will (well at one of the 30 stops).

It runs about every 15-20 minutes.

Dennis