Warren Falls is a popular local swimming hole just outside of Warren, VT on Route 100. You can access the falls by driving south on Route 100 from Warren (it's 3.5 miles south on the right hand side) or north from Granville on Route 100. The parking lot is clearly marked with a sign and ample parking even for busy days (summer and peak foliage). 

The path to the falls is only a few hundred feet from the parking lot and the best way to get down to the riverbed is to turn right and follow the path down a short hill, which brings you a bit further down stream to view the falls. 

You can swim here and many people do in the summer. If you're not planning on swimming, be sure to wear shoes/boots with good grip as the rocks are really slippery all year. Don't jump off the rocks, people get seriously hurt doing that every year due to the difficulty in determining depth. 

The best time to view the falls themselves is during the spring when mountain snow is melting, but the summer is great for swimming and fall is perfect for foliage. I haven't been in the winter yet, but I'm sure it's stunning and also easy to access since it's right on Route 100.