The Pumpelly Trail head is located on Lake Road a few miles past the center of Dublin, New Hampshire heading west on Route 101 (not far from Peterborough). Lake road is just before Dublin Lake on the left. There are no signs marking the trail head, but there will be cars parked along the side of the road about half mile on the left.
I teach aerobics three times per week and cycle about 50 miles per week. I think I'm in pretty good physical condition. My quadraceps and hamstring muscles were sore for several days after this hike. It took me about 2 to 2 1/2 hours each way to hike up and down. The first part of the trail is relatively flat. There are some rocky parts that require some crawling and climbing as you progress. This hike is a good workout.
Your reward at the end is being able to stick your feet in Dublin Lake or go for a swim.
Here's a link to the Google Map for the trail head.
In Peterborough, I recommend a few restaurants as well: Aqua Bistro (upscale but casual attire), Peterborough Diner, and Brady's Bar and Grill. I hear there is a Mexican restaurant that is good, but I haven't eaten there. The Peterborough Diner gives a discount if you on a motorcycle.