Bath is England's only entire UNESCO World Heritage city, built from pale gold limestone over a genuine Roman bathing complex still fed by natural hot springs. Georgian architecture — crescents, terraces, and Pulteney Bridge — frames a compact, walkable center on a horseshoe bend of the River Avon.
Late September through November for mild weather, fewer crowds than summer, and autumn color along the Crescent's lawns and the river.
Sally Lunn's serves a version of the Bath bun that's been made in the same house since the 1680s, and the Pump Room next to the Baths does a proper afternoon tea beneath chandeliers, with a live pianist most days.
Base yourself around Great Pulteney Street or the lanes near the Abbey, close enough to walk to the Baths, the Crescent, and the river in any direction.
Skip the daytime crowds at the Roman Baths and instead walk the river path from Pulteney Bridge to Bathwick at dusk, when the narrowboats and Georgian terraces light up and the tour groups have gone.
Read more in Bath Travel Guide: Roman Baths, Georgian Crescents & the River Avon.