This Achievement is not Missable but it is Buggy-.
If you have already completed:
you can return to the Underworld to finish this achievement, or any other quests, by going to the map, and pressing
to bring up the portals.
There are 17 Tartaros Rifts in 9 locations. You can use the Xbox One achievement tracker to track your progress (5.8% per Tartaros Rift sealed).
To seal a Tartaros Rift you have to enter it by pressing
and then kill all the enemies guarding it. For the ones below ground, you can use Ikaros to locate them before you enter. You gain 1 Ability Point for every Tartaros Rift sealed.The Scorched LandsAncient Temenos
2Lost Temple of Nyx
2Mourning FieldsCave of Despair
1Cradle of the Underworld
2Chasm of TormentRestless Nekropolis
2Pit of Deprivation
2Echoes of the Styx