Feel like enjoying a nice lunch & pint of ale in a crypt? Make your way to St. Martin in the Fields church in Trafalgar Square! Below is info from their website. I love how they call it an "unhurried atmosphere"...
IT'S IN A FRIGGIN' CRYPT!

The Cafe in the Crypt offers a welcome retreat from the hustle and bustle of Trafalgar Square. You can enjoy a cup of coffee, a glass of wine, a full meal or treat yourself to our traditional English afternoon tea. The Cafe uses fresh ingredients with the majority of our menu being prepared daily on the premises. We aim to serve fresh and imaginative food using the expertise and knowledge of our chefs from around the world. The unhurried atmosphere makes this the perfect place to meet your friends, sit and write a note or just rest a while from your hectic day. The Cafe was featured in the Top Ten of the '50 Best Places to Meet in London' (The Independent, January 2002)