I’ll start the 100 places with one I know well. It’s the Paine Estate, also known as Stonehurst. Landscaped by Frederick Law Olmsted (of Central Park and the Emerald Necklace fame), it’s mostly wooded (technically the Storer Conservation Land) with some fields as well.
There’s quite a few trails around the estate (maps are posted in several places and can be viewed here). The main one is the Bull Run Trail, which runs from the building itself to the high school parking lot. Most of the other trails are linked to the Bull Run in some way. It’s hard to get lost as you’re never too far from the Bull Run and it’s very obvious if you leave the estate.
One thing to note is that a lot of people walk dogs and not many follow leash laws. Fortunately, they tend to stay on the main paths and recent enforcement and new regulations has cut the problem somewhat. But stay on side paths and you should be ok.
I have a few preferred walks. One is to take the trail in the northeast corner of the parking lot up and left until it rejoins the Hobbes Trail that also starts in the parking lot. I then follow the Hobbes Trail to the vernal pool, taking the Hemlock Trail across. As the Hemlock Trail meets the Bull Run Trail, I’ll take Storer Path to the abandoned parking lot. After poking around there, I’ll work my way back towards the estate, staying to the right until I reach the field. That path can get a little wet in spring, but it’s usually passable. After wandering through the field, I head back, often cutting through the hemlock grove.
Other times I’ll head downhill from the parking lot on the Morrison Trail (southeast corner) and then follow the loop around at the bottom of the hill and then go back up the road. You can also take the uphill trail from the parking lot and then loop to the right and down the hill as well.
If I’m coming from the high school, I’ll follow the Bull Run trail and take one of the first two trails that run to the right. I’ll work my way along the edge and either rejoin the main trail or reach the old parking lot. I’ll often follow the Hobbes Trail on my way back.
The best birding is generally around the first route I described above (from the parking lot to the vernal pool to the old parking lot to the open field and around the building). However, things can be just about anywhere in the woods. I’ve had good luck right by the high school and and way down along the western edge (Storer Path).
Butterflies and dragonflies are best at the field to the west of the house, especially before it gets mowed early in the summer. The parking lot and surrounding area is also good. The middle of the woods is not, as expected, although several years running my first butterflies of the year have been between the abandoned parking lot and the stream. Jewelwings can be all over.
Bird highlights include Yellow-billed Cuckoos, which appeared to be nesting somewhere below the building last year, Indigo Buntings, many woodpeckers, and owls. I’ve had good luck hearing owls on Christmas bird counts, although I’ve yet to actually see one. However, my parents had a Great Horned on the count several years running.
Insect highlights include Indian Skippers, Painted Skimmers, and Ebony Jewelwings all over the place (may not be unusual but they’re so spectacular). I’m sure more time will find more good things.
My lists are on this website, available on the Paine Estate Nature page.
The parking lot is at the end of Gentleman’s Way in Waltham, which is off of Beaver St., right near the rotary. Follow up the hill and the lot is to the right. You can also park at Waltham High School. There’s almost always parking on the hill, even when school is in session.
Trails are fairly easy. One or two may be a bit rough and several get wet in spring. Most are marked handicap accessible, although I find very few of them actually are. Update: I figured out that the signs actually are indicating how accessible they are based on the angle of the line under the wheelchair. Most are therefore not terribly accessible, and I’m not so sure about the ones that are marked as flat.
The building itself is quite spectacular, it’s well worth arranging for a tour at some point.