How many secret levels are there and how do I unlock them?

I know there's at least one secret level, but I've been having a lot of trouble figuring out if there's any other secret levels. My google-fu is failing me, since any search for "Secret levels" just brings up details on the secret characters.

How many secret levels are there, and how do I unlock them?

There are two secret levels, Chopper Drop and Skate Heaven.

In my playthough, I just 100% everything starting with THPS 1 then THPS 2 with one skater which seems to unlock them both.

It seems the only requirement really is to get gold medals in all 3 competitions for THPS 2. That means, get gold for Marseille, Skatestreet, and The Bullring.