"Our town is after this bridge."

Translation: Наш город находится за этим мостом.

[khutch39]

после vs. за??

[Shady_arc]

"после" is a temporal "after".

"за" is linked to the concept of being "behind" or "following".

[richardensor]

Why "за этим мостом" and not "за этом мостом"?

[Shady_arc]

Here, за requires the noun to be in the Instrumental. Этот is an adjectival modifier and should agree to the noun it modifies in gender, number, and case. So it uses its masculine Instrumental form.

[Agelastos]

But isn't "етим" feminine?

[khutch39]

Feminine is этой in instrumental case. I find these types of charts helpful.
https://en.wiktionary.org/wiki/%D1%8D%D1%82%D0%BE%D1%82

[Skye530348]

Why; what did the bridge do?

[justTam0101]

When do we need "находится"? I thought in Russian you more or less skip the verb "to be". But when something is situated somewhere, we need "находится"?

[Shady_arc]

You do not need it. We use "is situated", "stands", "lies" somewhat more often than you would in English, but a zero copula is also OK.