There's a slight problem of scale here. The Ardennes Offensive or "Battle of the Bulge" wasn't fought on a single restricted battlefield. On 16 December 1944, the Germans launched an offensive through more than 50 kilometers of front line, covering nearly the entire Belgian-German border and parts of Luxembourg. The "Bulge" in the battle's nickname refers to the 60km deep salient that marked the Germans' furthest advance. You can see a map here. Bastogne is the encircled town on the southern flank of the bulge; some of the heaviest fighting actually took place on the northern flank, where the Germans had concentrated most of their tank divisions. In the top left corner of the map, you can see Antwerp, the ultimate goal of the offensive; if you were to zoom out only slightly further, you would see the North Sea.

The Ardennes Offensive was an operation involving dozens of divisions and hundreds of thousands of men. There is no way to represent this in a single diorama; you will have to select a slice of a particular engagement that took place during the battle. Some of it did indeed take place in forests, some in built-up areas like the towns of Bastogne, Malmédy, Trois Ponts and Sankt Vith. There was fighting in the Ardennes' steep valleys and on its fairly level plateaus, most of which are covered in hamlets and farmland. A simple Google search for images of the Ardennes Offensive will give you a sense of the landscape, buildings and weather conditions that defined the battle.