eniri

Eniri is en plus iri, and it keeps both parents' habits. You can treat it as transitive and give the place a plain accusative (eniri la ĉambron), or keep the preposition and put the -n on the noun after it (eniri en la ĉambron). Both are correct; the second is the older, more Zamenhofian shape. What you cannot do is write eniri en la ĉambro, because without the -n there is no movement and the sentence says you are already inside. Its opposite is eliri, and the pair enir- / elir- gives you enirejo and elirejo, the entrance and the exit on every Esperanto congress signpost.