Serenity Spa at Seaham Hall
Though this is technically a hotel spa, the off-the-beaten-track location (it's set on a clifftop, 20-minutes' drive from Newcastle) and extensive facilities mean it feels more like a destination in itself. Oriental in design, at its heart is a 20m ozone pool but there's also all manner of plunge pools, saunas, steam rooms and hot tubs. Not to mention a vast range of treatments.
Seaham Hall, Lord Byron's Walk, Seaham, County Durham, SR7 7AG
Spa breaks from £295 for two (sharing), including B&B accommodation and one treatment pp, booking.com