The 21 hectares (52 acres) of the formal Higashi Gyoen -- once the main grounds of Edo Castle and located next to the Imperial Palace -- are a wonderful respite in the middle of the city. Yet surprisingly, this garden is hardly ever crowded (except when cherry trees, azaleas, and other blossoms are in full bloom, or at lunchtime when obento-eating office workers fill the benches). Ninomaru, my favorite part, is laid out in Japanese style with a pond, steppingstones, and winding paths; it's particularly beautiful when the wisteria, azaleas, irises, and other flowers are at their peak. Near Ninomaru is the Sannomaru Shozokan, with free changing exhibitions of art treasures belonging to the Imperial family. There's also a bamboo grove, a rose garden, a plum grove, and an iris garden with plants introduced from the famous iris garden in Meiji Jingu.

On the highest spot of Higashi Gyoen is the Honmaru (inner citadel), where Tokugawa's main castle once stood. Built in the first half of the 1600s, the castle was massive, surrounded by a series of whirling moats and guarded by 23 watchtowers and 99 gates around its 16km (10-mile) perimeter. At its center was Japan's tallest building at the time, the five-story castle keep, soaring 50m (164 ft.) above its foundations and offering an expansive view over Edo. This is where Tokugawa Ieyasu would have taken refuge, had his empire ever been seriously threatened. Although most of the castle was a glimmering white, the keep was black with a gold roof, which must have been quite a sight in old Edo as it towered above the rest of the city. All that remains today of the shogun's castle are a few towers, gates, stone walls, moats, and the stone foundations of the keep.

Free guided tours of the garden and Marunouchi, run by volunteers, are given Saturday 1 to 3pm. Appointments aren’t necessary; just show up at the meeting point outside Tokyo Station’s Marunouchi Central Exit and look for the sign FREE WALKING TOUR.