Ash, 

It does use the subjunctive . ‘Nous …. entrions’ is the subjunctive present conjugation with ‘ nous ‘ of the regular er verb ‘ entrer ‘. 

Not to be confused with the imparfait, which uses the same word/is spelt the same way. 

The last link is to an answer related to this phrase as well, covering the use of present rather than past subjunctive.

https://www.lawlessfrench.com/verb-conjugations/entrer/

 Conjugate regular verbs in the subjunctive present in French (Le Subjonctif Présent)

 writing exercise, "The town of Gruyères", grammatical point