The land of Muspelheim is not very well-understood. Almost nothing is known about it save for the fact that it is home to the race of fire giants. Oh, and it's very hot there. But beyond that, the place is shrouded in mystery. The main reason for this mysteriousness is that the entire land is sealed off from the rest of the Nevernever. An (almost) indestructible barrier prevents all travel into and out of Muspelheim, except at one point. That point is known as The Gate To Muspelheim.
The Gate To Muspelheim is an uncomplicated area. It consists primarily of a black stone wall with a single gate. Behind it is Muspelheim, and nobody's really sure what it's like there. A river of magma serves as a moat for the wall, and beyond that moat the land is nothing more than a perfectly flat slab of rock.
The most important thing to remember about The Gate is its sheer scale. The wall is almost a full kilometre tall, and about five hundred metres thick. Plus, the stone that it is made out of is stronger than anything known to mortal science. The river of magma is about a kilometre wide, and an entire mountain's worth of molten rock flows through it every few minutes. This gate was built to hold off the attack of an entire pantheon of gods, and it lives up to that grandiose purpose.
On another note, the sky ends at the top of the wall. That's just the border of this particular universe. So nothing except an Outsider can possibly go over the wall.
Tunnelling won't work either, since there's actually nothing beneath the ground except an endless empty void.
To top it off, the wall is a threshold. And that threshold has been enhanced with a ward of truly absurd power.
But The Gate To Muspelheim is in fact a gate. People (and other things) are supposed to go through it sometimes. So the gate can be opened, and a drawbridge can be let down over the magma moat.
The wall is hollow in places, and almost two hundred fire giants live inside of it along with an army of Summer fey servants. They have plenty of room to spare, and guests are usually welcome.
The Gate To Muspelheim is the face that Muspelheim presents to the world as well as its first line of defence. So all diplomats who wish to bargain with fire giant-kind are invited here. If they survive the journey, they are greeted warmly (pun intended). But those who abuse the giants' hospitality are generally killed in very unpleasant ways.
Ironically, the incredible defences of The Gate are rarely used. The giants who live here love to fight, and when attacked they will usually let down the drawbridge so as to join the enemy in battle. This frankly stupid strategy has worked well in the past due to the great power of the fire giants, but it presents a hole in an otherwise (almost) impenetrable defence.
The Gate To Muspelheim is currently ruled by the fire giant Prince Urt and his Sidhe advisor Sir Lepid. Unlike most fire giants, Urt wants to change the world now instead of waiting for Ragnarok. He's gathered fire giants who either agree with him or simply want to kill things, and he's almost certainly preparing for a full-scale war.
