Students of the Clerical Arts know that casting the 'haven' spell anywhere in the world will transfer the caster to the nearest safe altar. What many don't know is that that casting the spell while already on an altar does the same thing, taking the caster to the next nearest altar. Often, that will simply bounce the caster between two altars, but some times it will take the caster on a longer journey.
Seen here for the first time outside of the Guild, is research showing the structure of the cross-haven altar network. Many worshipers of Set died bringing this information to the parchment- use it wisely!