Castles near London
20 castles sit within 40 miles of London - the Tower itself is on the doorstep, with Windsor, Hever and Leeds Castle further out into Berkshire and Kent.
Castles near Birmingham
19 castles are within 40 miles of Birmingham, from Dudley's ruined hilltop keep in the city's own backyard to Warwick's much-visited towers 20 miles south.
Castles near Glasgow
21 castles are within 40 miles of Glasgow - fewer than Edinburgh's count, and the city's own castle didn't survive, but Bothwell and Crookston are both a short trip out and genuinely worth it.
Castles near Leeds
15 castles sit within 40 miles of Leeds, spread across Yorkshire's ridings - Knaresborough and Skipton out to the north-west, Pontefract and Sandal closer to home, York's Clifford's Tower a short trip east.
Castles near Edinburgh
37 castles sit within 40 miles of Edinburgh, from the fortress on the doorstep to Rosslyn-country ruins out toward the Pentlands. Sorted by real distance, not a blogger's rough guess.
Castles near Liverpool
16 castles are within 40 miles of Liverpool, though most of the notable ones - Conwy, Flint, Chester - sit across the Welsh border rather than in Merseyside itself.
Castles near Manchester
Manchester is honestly thin on castles - just 10 within 40 miles, the closest a 20-mile drive out to Halton or Peveril in the Peak District. Worth knowing before you plan a castle day from the city itself.
Castles near Bristol
28 castles sit within 40 miles of Bristol, the second-highest count of any city on this list - Chepstow and the Wye Valley ruins just over the Severn, Cardiff and Caerphilly a little further into South Wales.
Castles near Cardiff
34 castles are within 40 miles of Cardiff - the highest density of any UK city on this list, courtesy of South Wales's cluster of Norman and Edwardian castles.
Castles near Newcastle
21 castles sit within 40 miles of Newcastle, including its own city-centre keep and the Northumberland coast fortresses a little further out.