For a long time, apartment rental trends had city dwellers looking for bigger and better spaces, but the latest trend in renting may surprise you: micro apartments. Micro, as in tiny, really tiny. We’re talking less than 400 square feet. Never thought you would live in a dorm-room-sized space after college? Think again.

While this hot rental trend may not make sense to those Americans that prefer wide-open spaces, for many renters, these tiny apartments make it possible to finally afford to live in the big cities they love.

New York City, for example, has notoriously high rents, but micro apartment buildings make it possible to live in the city that never sleeps for a fraction of the cost. And for many renters (who prefer to live alone and don’t suffer from claustrophobia), micro apartments with multi-purpose furnishings offer plenty of space.

Although the sizes are essentially the same, micro apartments can take many different forms. Hostel-style buildings, for example, generally give their occupants less than 200 square feet of private space–including the bathroom. A communal kitchen is then shared among several units.

Other micro apartment designs manage to squeeze a kitchen, bathroom and sleeping space all in one tiny box. Sound impossible? It’s not, but each space is approximately 40 percent smaller than it would be in a studio apartment.

There are several factors driving this apartment trend, not the least of which is a recovering national economy. Millennials in particular are accepting smaller salaries as they enter the job market, and may not be able to afford a cushy, spacious apartment. Still, that isn’t stopping them from pursuing their dreams of moving to America’s greatest cities, and that’s where the reduced rent of micro apartments comes in handy.

But these tiny living spaces are no longer just a rental trend–they’re a cultural phenomenon. YouTube videos of micro apartments have gone viral, and a new exhibition at the Museum of the City of New York called “Making Room” showcases the innovative design solutions emerging as a result of this rental trend.

And it’s only beginning. New York City alone plans to build 55 micro apartments this year, with move-in dates in September 2015. The city of Seattle has approved 48 micro-housing projects, and other major cities like Chicago are following suit. As long as people see value in living in the city and are looking for a bargain, this rental trend will likely continue.