This is the 16475th most frequent Polish word.
widokiem
"Widokiem" means "view" or "scene" in English, typically in the instrumental case in Polish.
The word 'widokiem' refers to 'a view'. It is used here in the instrumental case to describe the noun 'pokoj' ('room') as having a view of the sea.
Podobał mi się pokoj z widokiem na morze.
I liked the room with a view of the sea.
Here, 'widokiem' is instrumental, used to denote the feature of the park (i.e., it includes a view of the mountains).
Spacerowaliśmy po parku z widokiem na góry.
We walked in the park with a view of the mountains.
In this sentence, 'widokiem' in the instrumental case describes the house as being characterized by having a view of the lake.