Standard Loop (7 miles / 1660' vertical gain): This loop hike makes a good exploration of Wachusett Mountain State Reservation. First hike up to the summit of Wachusett Mountain and then down to Balance Rock. Then climb again, circling not quite back to the peak, on the west and south side of the mountain. Then finally descend, passing Echo Lake near the end of the circuit. On a clear day, the summit of Wachusett offers views to the Boston skyline as well as to New Hampshire's Mount Monadnock and Franconia Ridge.
This loop trail touches upon many of the paths in Wachusett Mountain State Reservation's network and finishes up with a half-mile walk on Westminster Road. Part of the route follows the Midstate Trail which is marked with both yellow and blue triangular blazes. The other paths are blazed just with blue. The system is well marked with trail signs at the many junctions
Infinity Loop (12 miles / 2500 ' vertical gain, submitted by Benjamin Masley): Inspired the Rainier and Shasta Infinity Loops, the idea is to create a trail map that ends up looking like a circle with a line intersecting it, all while starting and ending in the same position. I feel like it should be accepted that you can do the trail in any way so long as that is accomplished, but I'll describe the way I did this trail for the sake of there being a decent description of one way to do the route.
The route starts at the trailhead on Bolton Road. You climb up past Balance Rock and make your way to the first summit. You will have to cross a ski trail to do this. After summiting you begin your descent on the Jack Frost trail until you hit the split. We decided to take a left here (High Meadow Trail) to circle the mountain counter clockwise. You will take another left to hike the Bicentennial Trail that takes you by the Mountain House parking area, which has a water refill station. Walk the service road past the rental tent until you hit the paved summit road. Just after you start on the summit road you'll see a small parking lot on your right, here is where you can get on a small trail that runs next to the road. This will bring you out to the ski area. Walk through the ski area until you see the rental tent, past this is a service road that will take you back to the original trailhead (don't take the paved road). You don't have to go back to the trailhead here as you can continue on the loop.
This is where things get hairy. I took this trail as it was labelled on AllTrails (rookie mistake) as "Bolton Bond Bushwhack". There are a few rough trails you can follow in this bushwhack, but ultimately it will take you through some rough territory. At the end of the seemingly never-ending bushwhack, you'll climb a hill and come out on a wide trail called Balance Rock Road. Follow this to North Road, then to West Princeton Road. Take a left onto West road shortly after, and follow that to the Jack Frost trail. From here you will find your original path and take it up and over the summit and back to the trailhead the same way you came.
This trail includes roads, ski slope traverses, bushwhacking, a pond, a fire tower, and plenty of beautiful views. I highly recommend it!