Now that rumors are floating of 50km by 50km track building, let's see what forgotten course you'd bring back, I have several examples of old titans that need a revival.
Fuji Speedway's original layout featuring a huge banking. The course layout was changed since too many cars kept crashing on it but look how awesome it is and what'd it be like in vintage GT-Rs, Celicas, RX-3s, 240Zs, etc.
Monza, a track that needs no introduction. Imagine driving through previous versions with more modern and more powerful monster machines.
Autódromo de Sitges-Terramar, a surviving Spanish concrete monster oval from the early 20's that went silent in the 50's. Try running a NASCAR race on those banks.
Greenwood, because it's closest American circuit to Deep Forest Raceway and needs to be revived through the magic of digital rendering.