The one place I know of, that I know where it is on the map, that I've never been to, is Isabella Proud's Camp.
I keep missing this one too. Takoma is so far out of the way with no real reason to go there so I rarely do.
I've taken it a couple of times, but it clutters up the map.
Try using More Map Markers. It's really handy for fast-traveling to a spawn-free safe zone but I have so many map markers on my Pip-Boy that I sometimes have to dig through layers of markers to find the one I want. I'm a svcker for punishment. I can't play without it.
As for exploring, I have wandered on my own, gotten lost, searched for something I'd heard about and failed to find it, stumbled upon things by accident, and used directions from friends and the wiki. It's all good.