Last Friday, Waterstones hosted a sleepover for nineteen guests, who slept on airbeds with sleeping bags and took their pick of one free book.

Waterstones organized the event after an American tourist, David Willis, of Dallas, Texas, found himself locked inside the store in Trafalgar Square after employees had clocked out for the day. He frantically sent out a tweet to the store’s Twitter account for help, which caused the news to go viral, with thousands providing Willis with book recommendations and requesting, from Waterstones, an organized lock-in.

After Willis was freed at around 11:00 p.m., Waterstones responded quickly to the requests, and, according to The Guardian, “[made] the most of its embarrassment.” With Airbnb, they launched a competition for the overnight stay, which allowed guests to wander the bookstore and, in the morning, receive a free breakfast.

“There’s something really exciting about being in a bookshop when it’s dark and there’s no one else there, and it’s a bit out of bounds; like you’re an explorer and you’ve broken into a library,” said Clare Elcombe Webber to The Guardian, who, with her mother, slept over at the library.