This is the 178th most frequent Finnish word.
lähellä
Near; close.
In this sentence, 'lähellä' functions to indicate the nearby presence of the river relative to the walking action.
Kävelemme lähellä jokea.
We are walking near the river.
'Lähellä' here is used to indicate closeness or nearness in a more general or figurative sense, emphasizing proximity without a specified object.
Hänen työpaikkansa on ihan lähellä.
His workplace is very close.
Here, 'lähellä' is used as an adverb to describe the proximity of the park to the house.