The Fall of the Dungeon Guardians

The goal here is to go aaaaaaall the way back to level 8 where you almost escaped.

Make sure to open the shortcuts in all levels from 1 to 8 to make it faster, although you can still do it if you missed some of them, dont worry.

I think the trigger for this is reaching level 19 OR entering the secret room that connects floors 18,19 and 20.
You should do both for a safer bet.

Maybe you can do it once you can go back to level 1 from after level 13. (In Lvl 13, you can go go lvl 9 then find the warp back to lvl 1)
Once you are back (Probably because you found the 5th sword for the Treasure Hunt), go up to level 8 and try to escape through the NE stairs again.

Cheers

You can find the boots on Lvl 18, they are the Legendary Loot (LL) you can find close to an exit to level 19.

Basically, once you defeat the boss, open the gate at G then go west to Teleporter Tz but instead of going, drop to the north and move towards NE to the buttons.

Pretty sure you can get them earlier if you explore around the area.

Cheers!

Here is a map: