Where is PLUGINS in GIMP?

[Ofnuts]

Edit > Preferences > Folders > Plug-ins. This lists by default  two folders, one in the Gimp installation directory (somewhere under C:\Program files\GIMP\....) and one in your user files (IIRC, somewhere under C:\Users\{your_id}\AppData\Roaming). You can put the files in either, preferably the "user" one so that it's not wiped out if you need to reinstall Gimp.