From Discworld MUD Wiki
Periodically, wizards and witches like to try to break through to the Dungeon Dimensions, though there have been no recorded successes, although beings from the Dungeon Dimensions did break many arms and legs without fully coming through.
The attempt usually consists in casting a great many spells to raise the level of dynamic enchantment until the room enchantment is as high as possible. Damage and lost limbs makes casting harder above 1000 thaums.
Smashing thaum crystals can allow raising the room enchantment to 500 thaums which could help start new attemps, but subsequent smashings will bring it back down to 500 thaums.