The only freely accessible part of the Imperial Palace compound lets you wander among the mammoth stone walls that once constituted Edo Castle, the largest fortress in the world. Climb to the former keep foundation for elevated views over immaculate lawns and the broad moat below. The gardens blend Western-style lawns with Japanese landscaping and seasonal plantings — irises in June, chrysanthemums in autumn. It's remarkably uncrowded given its central location, a calm eye in the storm of Marunouchi's business district.