We need to know where you're coming from. I will assume you are coming from Denver.
To get to Barr Lake, take I-76 to Bromley Lane. Turn right. Go to Picadilly and turn right. The lake is on the right. Trust me - you'll see it.
For Walden\Sawhill take the Boulder turnpike to the Superior\Louisville exit. Turn right and go to South Boulder Road. Turn left on South Boulder Road and go to 75th. (This is the first light as you are going down the hill. Follow that until it comes to Baseline. Turn left. Take a right at the first light (This is still 75th - it just takes a little jog) Follow this until you come to Walden\Sawhill. It's on your left just after you cross the railroad tracks.