Sentence:  The difference between the approach to Baylen from the west and from the east, is that on the former side the traveller reaches the town through a semicircular <WSD>amphitheatre</WSD> of upland, while by the latter he comes up a V-shaped valley ... 
Meaning of the word marked with <WSD> tags:  A natural formation of a similar shape, where a steep mountain or slope a particular rock formation forms a partial or compete bowl, especially one used as a performance space (and possibly modified by carving out seats, etc) because the slopes naturally amplify or echo sound.