Forza Motorsport 3

Quickest way to get this and worked for me is to go to Free Play, Quick Race, pick a fast car (R1 class as they are the quickest), pick the shortest variant track at each track location. You don't need to win but must finish the race.

These are the tracks I done, in order:

Amalfi Coast Full Circuit
Camino Viejo de Montserrat Mini Circuit
Circuit de Catalunya School Circuit
Fujimi Kaido Stage C
Iberian International Circuit Mini Circuit
Ladera Test Track Mini Circuit
Le Mans Bugatti Circuit
Maple Valley Short Circuit
Laguna Seca Full Circuit
Mugello Club Circuit
New York Old Circuit
Nurburgring Stage A, B or C
Rally di Positano Stage B
Road America Full Circuit
Road Atlanta Club Circuit
Sebring Club Circuit
Sedona Raceway Park Speedway
Silverstone National Circuit
Sunset Peninsula Raceway Club Circuit
Suzuka East Circuit
Tsukuba Short Circuit
Motegi West Circuit

The clue is you have to 'race' so time trials and hot laps don't work.

The 2 downloaded tracks, Benchmark and Sidewinder can be ignored as they are not part of the achievement.

The only other way to unlocked it is through the season play mode. For some it has unlocked during season 4 or 5.

Hope this is of some help to you.

For those with the UItimate Edtion version of the game you must also race at

- Benchmark
- Nurburgring GP
- Sidewinder

Any track at these locations will do.
If youve done the rest of the track then these will be your last 3 , if it doesnt pop once a race is done at each of these locations youve still got another some where

There is a relatively easy way to ensure this achievement is unlocked during normal season play.

Everytime you get to select a midweek race type, always pick the option 'See New Race Tracks'.

If this option isn't there for some reason, then exit back to car select, choose a different car (doesn't usually matter which) and when you go back to seaon play there will be three different race events to choose from.

I can testify that in addition to the normal tracks if you have installed any DLC that contains a new track you must Race at least once on it, my achiev poped on after I finished the Sidewinder DLC track.