Prom here in my country is mainly for the senior class (they perform a special entry dance in matching dresses and then a midnight show which is dance, comedy etc), but everybody at the school (younger students, teachers, parents, relatives) gets to go as well. In the town where I went to high school, it was always held in a castle which was pretty cool. We have buffets, several bars, rooms for ballroom dancing and a room that´s turned into a "club". And the legal drinking age is 16 for wine/beer and 18 for hard liquor.
So yeah, those proms were fun, I went every year, but my personal prom when I was a senior was stressful cause we had to perform those dances and you had to entertain your family at the table etc.
Then I also experienced prom at a US high school when I was a junior. My date ended up not being able to go (what a shame, he was cute!), so I went with some friends. Overall, that prom was so lame. No food, no alcohol (of course lol), and I believe it was over at midnight or so (whereas ours last until 5am). Since my date didn´t go to prom there weren´t any afterparties I could have gone to with him, so I went to a "party" with this girl I knew. Little did I know this girl´s friends were conservative christians. The "party" consisted of watching TV in the living room & eating pizza. The parents were there at all times to ensure that at no point a boy and a girl were ever alone in a room together.