Here is the full list of all 99 Path of Achra achievements.
Pass through the Red Tower
Unlock the "Earth Mage" prestige class
Pass through the Violet Tower
Deal an instance of 1,000+ damage
Encounter the inevitable moment...
Pass through the Green Tower
Enter the land of Achra
Pass through the Obelisk
Kill the guardian of the Obelisk
Kill the guardian of the Astrolith
Pass through the Astrolith
Deal an instance of 10,000+ damage
Deal an instance of 100,000+ damage
Unlock the "Pyromaniac" prestige class
Unlock the "Champion" prestige class
Unlock the "Kashra" prestige class
Unlock the "Angiok" prestige class
Unlock the "Sahasi" prestige class
Unlock the "Samnite" prestige class
Unlock the "Arch-Magus" prestige class
Unlock the "Void Mage" prestige class
Unlock the "Blood Mage" prestige class
Unlock the "Mindpiercer" prestige class
Unlock the "Venite" prestige class
Unlock the "Shapeshifter" prestige class
Unlock the "Psychonaut" prestige class
Unlock the "Ice Shah" prestige class
Unlock the "Gothi" prestige class
Unlock the "Executioner" prestige class
Unlock the "Doomsayer" prestige class
Unlock the "Pain Cleric" prestige class
Unlock the "Paragon" prestige class
Unlock the "Oozemancer" prestige class
Unlock the "Stormbringer" prestige class
Deal an instance of 1,000,000+ damage
Unlock the "Exultite" prestige class
Unlock the "Mind Knight" prestige class
Unlock the "Arsonist" prestige class
Unlock the "Death Knight" prestige class
Unlock the "Surtmir" prestige class
Unlock the "Alizeh" prestige class
Unlock the "Dianmai" prestige class
Unlock the "Vengati" prestige class
Unlock the "Necromancer" prestige class
Unlock the "Mesmer" prestige class
Unlock the "Flame Knight" prestige class
Unlock the "Destroyer" prestige class
Unlock the "Gallus" prestige class
Unlock the "Frost Knight" prestige class
Unlock the "Liturgist" prestige class
Unlock the "Bheith Nochti" prestige class
Unlock the "Torturer" prestige class
Unlock the "Shantih" prestige class
Unlock the "Tamasa" prestige class
Unlock the "Ill Prophet" prestige class
Unlock the "Hazar" prestige class
Unlock the "Strijela" prestige class
Unlock the "Windblade" prestige class
Unlock the "Starjumper" prestige class
Unlock the "Topheth" prestige class
Unlock the "Arch-Lizard" prestige class
Unlock the "Plaguemancer" prestige class
Unlock the "Gliva" prestige class
Unlock the "Frenzied One" prestige class
Unlock the "Horror" prestige class
Unlock the "Mura" prestige class
Unlock the "Ormjarl" prestige class
Unlock the "Snakedancer" prestige class
Unlock the "Merzot" prestige class
Unlock the "Shazuza" prestige class
Unlock the "Damunja" prestige class
Unlock the "Uspori" prestige class
Unlock the "Berserker" prestige class
Unlock the "Dreamer" prestige class
Unlock the "Bolga" prestige class
Unlock the "Blood-drinker" prestige class
Unlock the "Worm-born" prestige class
Unlock the "Arborus" prestige class
Unlock the "Samsi" prestige class
Unlock the "Acolyte" prestige class
Achieve victory with the "Ur-Beast" prestige class
Achieve victory with only Fire powers
Achieve victory with only Martial powers
Achieve victory with only Lightning powers
Achieve victory with only Astral powers
Achieve victory with only Ice powers
Achieve victory with only Psychic powers
Achieve victory with only Life powers
Achieve victory with only Blood powers
Achieve victory with only Poison powers
Achieve victory with no powers
Achieve victory with only Death powers
Achieve victory with the "Anqarak" prestige class
Achieve victory with the "Uhrata" prestige class
Achieve victory with the "Night-Crow" prestige class
Achieve victory with the "Beastmaster" prestige class
Achieve victory with the "Elementalist" prestige class
Achieve victory with the "Suwag" prestige class
Achieve victory with the "Aqliyya" prestige class