Gran Turismo 6 user created tracks - a great one this, Knockhill in Scotland, kindly created for us by GT Planet member Fido_le_muet
https://www.gtplanet.net/forum/members/fido_le_muet.49606/
You can download the circuit here and I highly recommend it!
https://www.gtplanet.net/forum/resources/knockhill.1943/