The Diekirch District actually does not exist any more, it was abandoned in 2015. Before it was one of three districts of the Grand Duchy of Luxembourg, the northern part of the tiny country. There is no new structure instead of the districts, they were simply abolished. Each District contained a number of cantons which still exist unchanged.
The Diekirch District in the north is actually part of the Ardennes mountains, which are more like hills and consist mostly of slate. The only sights here are mines, there is no limestone for caves.