London’s most popular new family outing is like a DVD extra feature that comes to life; it’s a full day out, and 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 not much 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 by the craftsmanship of items that got barely 2 seconds of screen time. 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 Dr. and the actual Knight Bus, you’ll find one of only four places on Earth where you can taste Butterbeer and Butterbeer ice cream. And you won’t believe the gift shop. Easy 15min. trains (don’t get on one that takes 40 min.) 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 sells people pictures.) You will wait just outside the Watford Junction station for the shuttle bus.