The Azure Sun, also known as The Crystal, is the huge crystal in the centre of Yliakum's ceiling. It is the lower end of an enormous column of crystal, extending up to the surface world.
The Crystal draws its light from the surface, and thus Yliakum is subjected to times of day and night. The light is sufficiently strong for plants to grow on the higher levels, but is only just enough to penetrate the lake and light Yliakum's Seventh level. The amount of light also varies slightly over the year.
On rare occasions, the Crystal's light will completely disappear, an event known as an 'eclipse'. There seems to be a connection between these events and a crystal in the Death Realm.
Besides light, the Crystal also radiates magic energy strong enough to dissociate any matter coming close to it. Being shot to the Crystal has been used as a method of execution - such proximity to the Sun brings about certain True Death. The Crystal's magic is what attracted the gods Laanx and Talad to Yliakum, and was used to create the Lemur and Kran races.
The people in Yliakum can only see the lower end of the Crystal, and the magic it radiates prevents them from exploring its surface or any point close to it. Although there are many theories about their Azure Sun, Yliakum's inhabitants do not know much about it.