There are actually several floating doors in the Frigate level that are accessible if you perform a few glitches. The doors are left over from when the developers decided to turn them into doorways, but chose not to delete the doors for some reason. They still exist in the level's geometry, but only from certain angles.

In order to see them, turn on Tiny Bond from the cheat menu, and head for the first set of stairs heading down to the engine room. If you do the floating Tiny Bond glitch (crouch with R and C-Down) and walk down the stairs, you'll float over them and into the geometry of the level. Eventually you will see a door floating in space. If you open this door in mid air, go through it, and turn right, you will see a second door floating in mid-air as well. You cannot reach the second door without falling down, however.

If you plant remote mines on the floating doors, then go back around to the hallway and detonate the mines, they'll explode in front of you without any visible fireball. The explosion will merely send bits and pieces of debris flying everywhere.