Fourth Connecticut Lake Trail is a public trail maintained by the Nature Conservancy that criss-crosses the international border between the United States and Canada (New Hampshire and Quebec) for 0.6 miles (0.97 km) and ends in a loop around the Fourth Connecticut Lake in the United States. The Fourth Connecticut Lake Trail is one of the few international trails in North America. For US residents, identification and passports to Canada are not needed to go on the trail, since the trail starts on the US side of the international border and ends in the US, even though it does go into Canada.
Fourth Connecticut Lake Trail Wikipedia
The parking area for hikers is northeast of the U.S. border inspection building. The sign for the trail head is northwest of the U.S. border inspection building, and the trail begins just to its right (east). The trail has no cell phone coverage, requires some non-technical climbing, and starts at a good elevation, so one should be prepared even in summer.