Obscura Day

Atlas Obscura, an online compendium dedicated to the world's wonders, curiosities and esoterica, hosts this day of behind-the-scenes tours, performances and other events. London events include short film screenings from The Adventurists in the Royal Geographical Society's map room; a Hidden London walk uncovering the physical remains of the past such as the old Roman wall; and behind the scenes tours of the astrology and horology collections of the Royal Observatory. See the website for full details, including times and prices.