Four Xel'Naga towers rim the heart, as well as four in the direct center near the resource pit. Each player has two doorways, one that is double-sealed with rocks. beware lava surges as they will burn your units to a crisp. be cautious!
More In-depth, The lava will begin to flow 30-90 secconds after the last surge ends, Be sure all units (Even workers) are out of the lava, as it will burn anything in it to a crisp in a matter of secconds, During the surges, warefare will rarely commence as it cuts off all movement.