What other allegorical images are present in Dante's landscape?

I'm giving you part of a very good essay on exactly your question. Please follow the source-link to read the rest.

There are two distinct portions of the story Virgil recounts to the Pilgrim in this passage; yet a third image comes from the landscape surrounding the two as they talk. In all three sections, the pictures painted by the poets are geographically and topologically defined, with concrete depictions of the surroundings and a well-focused center. The river, for instance, which the figures use as a pathway through the deserted landscape, is at first seen through its environment, and its origins are specified. Dante then draws a comparison to a similar river in Italy; this concrete image, though not helpful for the modern reader, would have been significant to Dante's contemporaries. Finally, then, Dante describes the river itself, with its encasement of stone, and reveals its function for the travelers as a bridge or a path which they will follow:

Without exchanging words we reached a place

where a narrow stream came gushing from the woods

(its reddish water still runs fear through me!);

Like the one that issues from the Bulicame,

whose waters are shared by prostitutes downstream,

it wore its way across the desert sand.

This river's bed and banks were made of stone,

so were the tops on both its sides; and then

I understood this was our way across. (ll. 76-84)