London’s most popular new family outing is like a DVD extra feature that comes to life, and it’s as gripping as the fine museums can be. On the very lot where the eight movies of history’s most successful film franchise were shot, it seems that every set, prop, prosthetic, wig, and wand—and I mean every last thing—was lovingly saved for this polished, informative, and exhaustive walk-though feast. You could spend hours grazing the bounty, from the students’ Great Hall to Dumbledore’s roost to Dolores Umbridge’s den to the actual Diagon Alley. There’s little filler, so book your entry time for early in the day so you’ll have time to wander. Even if you care nothing about the movies, you will be blown away that items that got barely two seconds of long-lens screen time could possess such intricate craftsmanship. The finale, an astounding 1:24 scale model of Hogwarts Castle embedded with 2,500 fiber optic lights, is 50 feet across and takes up an arena-size room lit to simulate day and night. Midway through the tour, in an outdoor area containing 4 Privet Drive and the actual Knight Bus, you’ll find the only place outside of Orlando where you can taste Butterbeer (£3). And you won’t believe the gift shop. Easy 15-minute trains go three times an hour from Euston Station—but not, fans sigh, from Platform 9 3/4 at King’s Cross. (Although there, an enterprising Potter souvenir stall affixed a sign and takes pictures for £10.)