Cover illustration for The Map of Tolkien's Beleriand and the Lands to the North by Brian Sibley, HarperCollinsPublishers
Knowing that the back cover of the maps always need to support a lot of text, the creatures approaching Gondolin are black on black. Balrogs and dragons for the most part.
Quite a lot of work can go into the portions of a cover which remain invisible or barely so once printed. They are always the most fun to do.
More New Zealand landscape here... Gondolin really could be hidden somewhere in New Zealand's South Island...