I have my filament in a drawer beneath the Prusa Mini, nicely tucked away, but obviously the filament is not a straight line to the printer. This is drilled into the table's corner with a #6 screw and guides the filament smoothly with a 608 bearing.
Update: Nov 6 2022 - Made some upgrades! Added a loop so the filament doesn't pop out if it's particular springy, and added some angled guides since I have a few sources of filament now that aren't always right in front of the printer.
Included is an 8mm shaft for the bearing, one side is slightly tapered to slide nicely into the side of the guide shown in the picture.
Print as-is from the STL. The overhangs are minimal, and don't require supports.
The author marked this model as their own original creation.