Guests at the Generator in Barcelona sip mojitos in the lounge, dine on tapas at the café, and take in the Spanish sun from personal balconies. It may sound like a fashionable boutique hotel, but visitors here are actually shacking up at a youth hostel.

Modern hostels with rooftop yoga, dance lessons, and specialty cocktails are popping up in London, Paris, Berlin, Venice and other large European cities.

These lodgings are a far cry from what traveling college students on a shoestring budget may recall years ago, when youth hostels meant sharing bare, cramped quarters with a communal bathroom down the hall.

Now, some of Europe’s biggest hostel owners and operators are trying to replicate their success across the Atlantic.

They are aiming to transform the disparate U.S. hostel scene from a collection of mom-and-pop operations to a business run more like a hotel chain.

“Hostels in the U.S. have…