„With sea view“ can sometimes be seen, but it's much less common than „with a sea view.“ – see the Ngram. There may be three (or more) explanations why „with sea view“ (without the indefinite article} can be acceptable or can be found.
- „With sea view“ is felt to be a kind of „adverbial set phrase“ like "a hotel room with [an] ensuite [bathroom], a hotel room with [a] wi-fi [connection], a hotel room with [a] mini-bar.
- „With sea view“ is felt to be part of a „list“ and we're therefore using a kind of „shorthand“ style which allows us to omit words that are not absolutely necessary to the meaning, so:
- for 100 euros, you can expect a room with sea view, wi-fi, ensuite, mini-bar and air conditioning. [ this is „list“ style].
3. The writer wasn't a native English speaker and just ran his text through a translation site with this result: pokoj s výhledem na moře – room with sea view ☹️
In normal full prose style, we wouldn't omit the article, so:.
- The hotel was lovely, we had sea view from the window …
- The hotel was lovely, we had a sea view from the window …