The Schmadribach Falls,1821-2. The falls are in the Lauterbrunnen valley in Switzerland (see the photograph below); Koch himself was Austrian.
The Wetterhorn from the Reichenbach Valley, 1824. This is where the famous Reichenbach Falls are located; here is a watercolour painting of them by Turner, from 1804:
This is of course where Sherlock Holmes was supposed to have met his death (at least until Conan Doyle was obliged to resurrect him)! This is Sidney Paget's illustration of the episode.
Finally a photograph of the Schmadribach Falls, to compare with Koch's painting of them.