This is where the dragons went. They lie... not dead, not asleep, but... dormant. And although the space they occupy isn´t like normal space, nevertheless they are packed in tightly. They could put you in mind of a can of sardines, if you thought sardines were huge and scaly. And presumably, somewhere, there´s a key...
GUARDS! GUARDS! is the 8th Discworld novel - and after this, dragons will never be the same again!