There are absolutely great holidays in Europe, especially for 18 year olds. In Europe, 18 is the legal age to consume alcohol, and there are plenty of parties to pick from. But seeing your age, and assuming this is your first trip abroad, keep your witts about you.
There’s a great website called www.nomadnightlife.com that posts nightlife events, pub crawls, city cards (which are a God-send), food/drink related activities, and recreational stuff - all at discounted prices for about 5 different major European cities.
A great feature that makes this site special is how it meticulously analyzes every single venue in all of the cities it has on there, and disqualifies any that have reports of staff physically harming guests, staff/local club goers ripping off English speaking guests, any kind of “bouncer discrimination” towards non native speakers, and more.
Backpacking Europe is a blast, I’ve done it more than once. You’ll meet so many interesting people from all around the world at all of the offbeat hostels and lively venues. It’s an experience I think everyone should undergo at least once in their lifetime. That being said, it’s always important to have a reliable and trustworthy resource(s) to help ensure your betterment, security, and overall level of enjoyment.
Happy Travels!