Inside my long string of numbers and letters file, the thing taking up most of the room is the "proxies" subfolder, which in turn has two subfolders "720p" and "2560" and that 2560 one is taking up more than 25GB.
I don't even know why because I store my originals to an external SSD. Any ideas?
The proxies are used for display on your monitor and make the application more efficient when viewing thumbnails in the grid (G) view or full screen in the detail (D) view. 720 will probably be video files and 2560 will be the smart previews for image files. So you should always see an efficient streamlined view even if your external SSD was temporarily disconnected from your computer.
Proxies are previews with the edits applied, so you can see what you have done to the images. Lightroom is a non-destructive editor, which means that your originals are untouched. That's why you still need proxies, even if you have saved a local copy of the originals. If Lightroom would show you the originals, you would see unedited images.