The part of the Eifel that lies in North Rhine-Westphalia.
The Eifel is a low mountain range bordered by the Rhine to the east and the Mosel to the south. The scenery includes some interesting formations caused by volcanic activity such as circular hills formed from vents and circular lakes in old craters.
Traveling through the Eifel is possible all year long.
No shocker, people in this region speak German. Nevertheless, most people can speak English to varying degrees; older people might barely know how to say a few words, whereas the majority of the younger generations can hold a basic conversation.
Thanks to its geographic location, you might come across people that can speak some French, Dutch, or both.
By train or you might take buses leaving from bigger cities (e.g., Aachen) or leaving from the train stations.
Best by buses, local trains, or cab.
Many marked hiking routes, circular and long distance through the area.
Cycling. Many signposted bike routes through the region.
This area of Germany is usually safe. As a city that sits on a tri-point border, Aachen might have a few issues.
Related Wikipedia article: Eifel