An ancient part of England
Close to Keswick, in the Lake District, you can find one of the most ancient places in this part of England, the Stone Circle of Castlerigg. It dates back to prehistory, and is free to visit. It's not the biggest or most impressive stone monument, but it is the oldest in England, constructed around 3000 BC, in the Neolithic era. It stands on a hill between valleys, giving it stunning views, with major peaks on each side, the mountains of Helvellyn and those of High Seat.
Another thing worth mentioning is that the whole circle is still in fairly good condition, which isn't easy. There are almost always strong winds in the area, reinforcing the mystical atmosphere and invoking the forces of nature that were once believed to be the work of the gods.