Great Brook Farm State Park in Carlisle, MA, is one of the true gems of Eastern Massachusetts. It is a vast area that includes deep woods, low hills, farmland, meadows, streams, and beautiful bodies of water such as Meadow Pond (see photo). Great Brook Farm is also a four-season recreation area, as it has cross-country skiing and snowshoeing in the winter, and hiking and horseback riding for much of the rest of the year.
The trail network at Great Brook Farm State Park is extensive, allowing outdoors lovers to really get deep into some rugged land here. One particularly scenic loop is to start at the Hart Barn and Ski Center at the Lowell Road parking lot, and head clockwise along a number of trails, including the Lantern Loop, and Litchfield Loop, and the rugged Stone Row trail. From here, a short side trip can be taken north into Chelmsford, where a trail runs alongside the serene Russell Mill Pond (see photo). From this short spur, hikers can continue on to the Woodchuck Trail and the Garrison Loop, where there are a few historic sites to be seen.
From the Garrison Loop, hikers can turn left and cross North Road, taking the mostly level Pine Point Loop around Meadow Pond. A couple of interesting side trails with water views branch off of the Pine Point Loop, including the Beaver Loop and the Keyes Loop. Just before the Pine Point Loop enters a meadow area (where other trails can be taken back to the parking lot), a tree-shaded area around a boathouse (see photo) affords great views of the pond, and is an excellent place to have a picnic lunch. From here, it is an easy walk back to the parking lot.
Locke Pond is a bucolic, remote-feeling body of water in the Whipple Hill Conservation Area that straddles Winchester and Lexington. Many people who hike around Whipple Hill never even make it down to Locke Pond, as the sweeping views from the hill are often enough for folks who come to this rugged area northwest of Boston. 
One particularly nice approach to Locke Pond is from the aforementioned Whipple Hill. Park at the little pulloff on Johnson Road right where Winchester and Lexington meet, hike the few hundred feet up to the top of Whipple Hill, then go left from the summit, descending into the woods along a switchback trail that eventually straightens out, ending at a ravine just north of the pond. From here it is a very short walk to Locke Pond, where a number of trails afford excellent views.