Lessing did a lot of landscapes but my favourites were the ones in which he included castles and other buildings, and his 'Castle on a Rock' is excellent. His lighting and overall mood is somewhat mystical and the landscape is wonderful. This whole place tells a story; I interpreted it for a game where the PCs had to reach the castle via boat (as in the picture) and the castle was abandoned and had been built to keep incredibly dangerous people imprisoned.
If you put Karl Friedrich Lessing into Google Images you'll get lots of amazing pictures. There are some really inspirational paintings that will get your imagination going and you'll be able to give each location a story you can use in your game.