Schijen, the one which is in GL, SZ and UR
There aren’t very many mountains in Switzerland where you can walk around the summit and at the same time visit 3 different cantons. The [http://www.hikr.org/dir/Schijen_4662/ Schijen] is one of them. At P.2610 the 3 cantons Glarus, Schwyz and Uri join up. The path up there isn’t very easy no matter how you go up there...