The Pak 43 was the most powerful anti-tank gun of the Wehrmacht to see service in significant numbers. Three of these canons can still be found in the Ardennes (Hochfels, Wiltz and Troisvierges). This one is in a pretty bad shape and is located near the panoramic view of Hochfels. 

Probably knocked out in the Battle of the Bulge and placed here as a monument. Note that somebody has cut of the Muzzlebrake. It is standing as a silent withness of this battle in december 1944.