Wilts, Somerset and Dorset - an early line from the GWR▸ London to Bristol line, turning off at Thingley Junction and running via Trowbridge and Westbury (first line there) then on to Frome, Yeovil, Dorchester and Weymouth. Branches added later.
The London and South Western Railway reached Dorchester (South) too and the original platform was layed out there to let the line carry on straight ahead. However, that never happen - it's said to be because the other line was in the way blocking it, and it turned sharp left to join that line to Weymouth. Within my memory, trains from Weymouth to London ran round the curve at the station and reversed into the straight platform.
Map
GWR "Great Way Round" in mustard
LSWR▸ "Castleman's Corkscrew" in sage (section not built in dashed lines)
Wilts, Somerset and Weymouth in maroon
Later, shorter routes in thin navy