Magma Barracks

Spawns

 * Evolved Lemurian
 * Wisp
 * Bighorn Bison
 * Mechanical Spider

Bosses

 * The Direseeker
 * Cremator
 * Toxic Beast
 * Scavenger

Artifact
The artifact gate appears at the far left, on the middle level. Three switches are located in the level (example on the right). The switches are activated by damage, but as they are behind walls it's necessary to use an attack that can reach through the wall. Confirmed ways to press switches: ( no longer reaches the switch.)
 * Most? attacks paired with Brilliant Behemoth
 * Cremator's artillery shots (guide them by being near the buttons when Cremator aims a volley)
 * Most? attacks paired with Brilliant Behemoth
 * Cremator's artillery shots (guide them by being near the buttons when Cremator aims a volley)
 * Most? attacks paired with Brilliant Behemoth
 * Cremator's artillery shots (guide them by being near the buttons when Cremator aims a volley)

Two of the switches are located in the open at upper left and center of the level, while the third is hidden partway down the left-most narrow shaft and requires a little timing to activate. Note that the switches appear on the map variant that does not have lava at the bottom of that area (i.e. not Variant 1 depicted below).

Once all three switches are activated the Sacrifice artifact will appear on the gate.