Did they actually push through the forests and the large hills of the Ardennes “fabled” by the french impassible, or did they still go through the Ardennes but just by paved roads?
From what pictures I’ve seen the trees were quite old, so I don’t expect a Tank could blitzkrieg through there, and if it would it would give the French enough time to defend which is not what happened.
Okay, first of all when an army deems an area impassible it does not mean that you literally can't go through it. You have to keep in mind that the invasion of France contained over 3 million germans soldiers. Impassible in that context merely means that it was deemed unsuitable to attack through with significant forces. They were well aware that the Ardennes could be crossed as several divisions had dug in on the Meuse around Sedan.
Of course the tanks did not "blizt through trees", the majority of German armor at this point was light tanks, in many cases out-dated and a significant portion were booty tanks captured primarily at the annexation of Czechoslovakia, they could not smash through trees. Tanks in generally are not particularly well suited to attacking through dense forests.
There were plenty of roads, even towns, in the Ardennes but the road network was old and not suited to transport and supply a large force. It is in this context you have to understand the word "impassable". The French felt their position on the Meuse river was strong. Several divisions had dug in around the town and the advantageous ground allowed them to contest any attempt at crossing from well prepared positions with heavy artillery support. However, this plan was based on the assumption that a few divisions at most would cross the Ardennes and attack at Sedan.
What actually happened was that the Germans stacked divisions along every god damned road in the Ardennes virtually from Bitburg in Germany to the French border. This was a dangerous gamble. The German formations were neatly lined up on the road, unable to move and unable to take cover. In fact they were even spotted by reconnaissance aircraft prior to the attack. A second flight was ordered which confirmed that the roads were clogged with German divisions but French command still felt that the main attack would come further north and committed their bombers in support of the armies further north. Had they attacked the German formations in the Ardennes on the 12th or 13th of May it could well have resulted in an absolute slaughter that would have decimated Germanys elite armored and infantry divisions.