Skiing. White Tail. Used to take my kids there. Pass through clear spring. I believe this is west of camp David. Whites Ferry & Rockville are not close.
Radio tower?
https://www.airnav.com/airport/KHGR
Nearby radio navigation aids
VOR radial/distance VOR name Freq Var
HGRr091/(6.0) HAGERSTOWN VOR 109.80 07W
THSr150/17.0 ST THOMAS VORTAC 115.00 07W
MRBr023/20.2 MARTINSBURG VORTAC 112.10 07W
FDKr326/(24.1) FREDERICK VOR 109.00 08W
EMIr298/36.9 WESTMINSTER VORTAC 117.90 08W
Where? I’ve lived in MD even longer and spent lots of time in the woods. Never saw any tunnels. But Blair witch was filmed here
Howdy neighbor!