Hey, I finally get to correct AlanB
I live in the Denver area and don't have a car, so I use RTD a lot to get around. RTD includes light rail, buses, and door-to-door services like Call-n-Ride (
http://www.rtd-denver.com/SpecialRides/cal...Ride/index.html), and is in my opinion one of the best public transportation systems in the country. The buses and light rail generally run frequently and on time, and the system is very user-friendly. RTD offers a variety of day passes, depending on how far you wish to travel (
http://store.rtdpasses.com/, though you don't have enough time to order online). To purchase a day pass and to pick up an RTD system map, walk two blocks over to Market Street Station -- a big RTD regional hub. If you're going to be exploring downtown Denver, definitely make use of the free MallRide (
http://www.rtd-denver.com/Projects/Fact_Sh...lRide_Facts.pdf): it's a hybrid electric bus that runs from one end of downtown to another with a frequency of a couple of minutes, departing from Union Station. If you're interested in traveling farther afield, like, say, Boulder (highly recommended), take the B bus from Union Station -- it runs every half an hour on Saturdays.