Answer:
"along," "by," "through"
Explanation:
The sentence "caminamos por la playa" can be translated to "we walk along/through/by the beach", it depends on the context.
The preposition por has many different uses, one of them is to describe travel or motion. Por is used to refer to travel or motion through a place or location. So in this case, the sentence is referring to a motion (walk) through a place (the beach).