Each mission introduces new ways to use the environment.
Locate your save folder (usually in C:\Program Files (x86)\Steam\userdata\[User ID]\205930\remote ). Back up your original save. Replace it with the downloaded 100% save file.
When searching for an unlock link, you will likely encounter sites promising a small file that "instantly opens the map." Be cautious:
Disable Steam Cloud Sync temporarily so the game doesn't overwrite your new file with the old one. 2. Playing on "Easy" for Speed