Many monsters, creatures and beings live in the lands in and around Britain. In ancient times they were numerous, but as the age of man took hold most of them dwindled or hid in forests and dark places.
During Uther's time monsters began getting more common but it was during the age of Anarchy that the creatures of old really began taking hold.
These creatures are beyond the normal world or that of faerie or any other realm. They are creatures of legend and history in their own right.
These are classical monsters, creatures and dangers. They could be anything from the undead to the predatory monsters of old.
Sometimes the normal world of men can be scary enough as it is. Nature produces many monsters of it's own.