Hot off the heels of its London expansion and a $23 million Series C round, last-minute hotel booking app HotelTonight announced that it has hit a new milestone with three million downloads.  Additionally, it’s adding 10 more cities to its line-up, bringing its total to 50 cities worldwide.

The new cities include Birmingham, Edinburgh, Glasgow, and Liverpool in the UK.  In the U.S., HotelTonight now has partnerships with hotels in St. Louis, Charlotte, Pittsburgh, and Nashville.  Manchester and Salt Lake City will be added in early September.

To recap, the app does exactly what it says it does: it gets you a hotel—tonight.  And it does it without needing much input from you.  Where booking with Expedia or some other online company requires planning ahead, HotelTonight uses your location to find available rooms nearby at deep discounts—up to 70% off the standard price.  And it’s a win for hotels, who can fill unsold rooms at the last minute.

Back in June, HotelTonight launched its overseas expansion with its first city in the UK: London.  The move came just in time for the London Olympics, and co-founder and COO Jared Simon says that it was a “smashing success.”

“Hoteliers had long expected every room in London to be sold out well before the events began, and as a result they raised their rates significantly in the run up to the Olympics.  For various reasons, advance demand ended up being much softer than expected, and on the eve of the Games many rooms still sat vacant,” Simon told me.  “Prior to HotelTonight's arrival in London, there would have been no effective venue for hotels to move that extra inventory at the last minute, but HotelTonight gave hotels an ‘escape valve’ that allowed them to promote that inventory at discounted, yet still profitable rates to move rooms quickly.”

A recent survey from TripAdvisor found that 60% of mobile phone users have downloaded a travel related app, and 42% have used travel apps to research or book a hotel stay.

HotelTonight isn’t the only hotel-booking app on the block.  It’s contending with some big names, like Priceline and Hotwire.  But HotelTonight’s focus on last-minute bookings means users have to actually wait until noon to book a room that night, which equals cheaper rates and filled rooms for hotels.  And all of the hotels are personally vetted by HotelTonight staff, so you don’t run the risk of booking a room with a bed bug infestation.  Gross…

HotelTonight is available for free on iPhone, iPad, and Android.