There are several watch towers on Cam Lao Nam that are placed too high/ not sunk enough in the ground, and thus have inacessible ladders for infantry units.

South of Saigon:
Grid 167032
Map position [16709.5,3235.54,0]

Near Rach Gia:
Grid 154028
Map postion [15400.4,2839.25,0]

Around Cu Chi:
Grid 147054
Map position [14752.5,5496.59,0]
Grid 145057
Map position [14591.9,5722.92,0]
Grid 149057
Map position [14953.9,5697.5,0]
Grid 151058
Map position [15104.5,5817.36,0]

Aroun Tan Di:
Grid 090123
Map position [9031.81,12317.9,0]
Grid 089124
Map position [8967.37,12478.8,0]

East of Sang Ha, around the rocky mountain/PAVN camp:
Grid 025151
Map position [2529.06,15137.2,0]
Grid 028156
Map position [2883.95,15610.7,0]

In Phok Ham:
Grid 022133
Map position [2251.33,13394,0]