Here is the full list of all 36 Tony Hawk's Pro Skater 1 + 2 achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Unlock School in THPS1 Classic.
Earn a Medal on any competition park in Tours.
Unlock Roswell in THPS1 Classic.
Find every alien plushie.
Complete every goal in THPS1 Classic and gain all gold medals.
Unlock School II in THPS2 Classic.
Earn any 4 Medals on competition parks in Tours.
Unlock Bullring in THPS2 Classic.
Get hit by the Bull in Bullring.
Complete every goal in THPS2 Classic and gain all gold medals.
Complete a match in multiplayer.
Get hit by a vehicle on every map that features them.
Create a skater using the CAS system.
Create a new park and upload it.
Spend $10,000 in the Skate Shop.
Find all Stat points for any Pro Skater.
Unlock Officer Dick.
Earn the "Rookie " Challenge Collection.
Earn the "Veteran" Challenge Collection.
Earn the "Legend" Challenge Collection.
Complete all "Hard" Get-Theres.
Reach Career level 10.
Reach Career level 100.
Paint 100 surfaces in Graffiti across all playtime.
Give 50 Letters in Horse.
Land a 50,000+ point combo.
Achieve a High Score of 1,000,000+ on any classic Park.
Land a 1,000,000+ point combo.
Earn a score of 10,000,000 in any park in a 2 minute session or single combo. Game Mods must be disabled.
Complete all Gap collections.
Place 500 objects in CAP.
Bail a 100,000+ point combo.
Earn 5,000,000 points in Trick Attack across all playtime.
Earn 2,000,000 points in Combo Mambo across all playtime.
Break 20 Panes of Glass.
Achieve a judge score of 99.9 on a competition run.