In the west country, there are a number of options for turning a steam loco:
Bristol - A number of maneuvres available around the Temple Meads area via the triangular junction (wye) to the east of the station or St Philips Marsh depot 'balloon loop'. Triangular junctions galore exist around Parkway/Filton.
Westbury - The triangular junction at the east end of the station.
Salisbury - The triangular form junction to the east of the city known as the 'Laverstock Loop'
Yeovil - Railway Centre turntable.
Taunton - West Somerset Railway triangle (wye) at Norton Fitzwarren or turntable at Minehead.
Paignton - Dartmouth Steam Railway turntable at Churston.
Plymouth - The triangle at Laira depot.
Cornwall - The turntable at St Blazey depot, near Par.
There are also a number of itineraries that allow a turn en-route such as London to Exeter out via the GWR route and returning via the LSWR or vice versa. Similar possibilities around Bristol and Laverstock loop. The Bath, Chippenham, Trowbridge sub-network also forms a large triangle that could plausibly be used as a turning triangle for a loco or leg(s) thereof used as part of a circular itinerary for a complete train. Arriving from the Bristol direction, an excursion can also circumnavigate the Southampton area via the main station and return to Bristol, turning en route via Eastleigh - Romsey. Moving eastward along the south coast, there are more turning options but that's getting outside my stated 'west country' frame of reference.