Fly to Denver Inernational Airport. The Boulder Airporter provides regular service between the airport and Boulder for about $15. Dropoffs at hotels or the University is cheaper than door-to-door service. The supercoach provides competing service.
If you're renting a car, you take Pena Blvd out of the airport, which eventually feeds into I-70: go west. In about ten miles this will intersect I-25 which you take north. In a couple of miles, US36 exits to the right - and then immediately turns hard left over I-25. US36 brings you right into Boulder. The first stoplight is Colorado Blvd - the University is left at this light. Duane Physics Bldg is about a half mile west on this road - two tall towers attached to a long, L-shaped building. Parking is sometimes available on the street, or there's a parking garage back near 36 - on Regent Drive.
nick@ganesh.colorado.edu