The map vote rolled a dungeon. For the next ~15 - 20 minutes there are no traitors and no innocents - everyone on this server is on the same team, and the whole server is fighting monsters and bosses.
Three broken cube relics sit around the ruin, and three stone plates are waiting for them. Shove each cube relic onto its matching plate - they are physics props, so shooting or walking into them moves them. All three down at once breaks the seal.
Nothing spawns until that happens, so the run does not really start until the group is ready.
A pillar climbs while enough players stand next to it - one on a quiet server, up to four on a full one. Step away and it slowly settles back down, so somebody has to hold ground.
Toads and Vesparok pour in from the ruins the entire time, and the swarm thickens the higher a pillar gets. Split up: one group on the pillar, one group on the swarm.
Pushing a pillar past a threshold wakes a miniboss - a giant toad or a Vesparok. Killing one is a checkpoint: everyone gets crates, everyone is healed to full, and dead players are pulled straight back into the fight.
Rare finds live here too: Relic of Orddu, Crystal of Calesvol, Old World Artifact and the miniboss pets all drop from these kills.
With all three pillars up, the gate at the back of the ruin opens and every enemy on the map dies. Walk in with your team - once half the server is through the gate the fight starts and the doors shut.
This is the point of no return. Read the next section before you walk in.
Death is cheap during the pillar phase. You drop, you watch for thirty seconds, and you are put back on the map at full health. A timer on your screen counts it down. Re-equip your loadout from your inventory and get back in.
Once the boss fight begins, the thirty second timer is gone. If you go down you stay down until the run is over - but you still collect your end-of-run loot, so a death late in the fight is not a wasted hour.
Minibosses and Oxylus pay out large lumps of loot on top.
Loot orbs also drop off enemies as you kill them - run over them, they are yours alone and nobody can steal them.
Oxylus dies, the timer runs out, or the whole server wipes. Any of the three ends it.
A results screen shows the run, then your drops land in your inventory automatically.
About twenty seconds later the normal TTT map vote opens on this same server.
Next map is regular TTT again - traitors, detectives, the lot. Nothing carries over.