Availability: Every 15 minutes.
Pretty easy to solo, and easy to camp, CPK rooms on the way so be careful.
Preparation
Check your mems are ok before going, and restock reagents if you are low.
From Before the Mighty Fountain of Life go one room north, three east, twelve north, one more east, and two rooms northeast. Kill the burly guard for an iron gate key. Unlock the east and move one room east, two south, one southeast, three east, two northeast, and one north. Search in this room and open the east that gets revealed. Go one room east, one down, two west and wait at the dizzy room to be teleported. You should be teleported to a Damnation area.
This area has a series of dizzy rooms all named Damnation. They are all silenced rooms and NPK. Generally the best strategy is to just try spamming a direction towards any of the corners of the area. NW, SW, NE, SE. They are all named Above a Fiery Abyss. All the corners will teleport you further into an NPK room named Hall of Gath. Kill all the fire-breathing salamanders in that room, and in the room to the north and east of it. Also kill the robed followers of Gath in the east room.
The High Priestess of Gath encounter
The High Priestess of Gath should be one room west of the room named Hall of Gath. The reason that you need to kill all the salamanders and robed followers is so that they won't walk into the room east of The High Priestess of Gath which is a private room and would prevent you from fleeing from the Priestess. Also note that her room is CPK and a solitary room, so you can not be attacked by other players. However, your corpse can be looted quite easily by other players. Additionally, the room to the east of her is private, so you can be easily blocked from fleeing. She is not aggro so you can cast calm when you get low on hit points if you need to, but she does cast tremor and harm so be sure to calm while she's not casting. You can dispel her with a weapon if you want. She's not too hard to kill. You can also use a toy soldier for extra damage if you choose. You can also spell her up quite easily with curse, weaken, plague, poison, web, and faerie fire. She deals bash damage and casts spells like plague, poison, tremor, harm, and blindness. Just spell her up and heal yourself and/or cure poison/plague during combat or you can cast calm cure poison/plague and heal. This way you won't end up without spell points in the middle or at the end of combat. Enervation does not work on her, but pretty much every other type of damage does work.
If you can't walk out because of other players blocking the way out you will not be able to use Word of Recall, home recall, gohall, or a puzzle box to get out. You can however use a featureless white cube or a black moonstone to get out if you are trapped at the Sacred Chapel of Gath. If you're not trapped in you can just walk east one room and then north one room and go up to use one of the portals to get out. The Gath temple trainer is located one east and one south. This is now a NPK room.
Note: This is the trainer for Augment Aura and Sanctify.
The High Priestess of Gath carries
Item 'a holy symbol of Gath' is type ankh, alignment -300, made of obsidian, has keywords 'holy symbol Gath', equipped around the neck. This item weighs 0 stones and 11 pebbles, and is valued at 41,500 gp. This level 120 item has the attributes: identified invis no-auction insulated A holy symbol of Gath is in excellent condition. Affects wisdom by 2. Casts the level 78 spell, 'bless'. Casts the level 78 spell, 'fireshield'. *This item may be repaired 5 times. This holy symbol of Gath is made of a pure obsidian stone and has been blessed by the high priest of Xaventry. Giving its wearer the blessing of fire, whomever wears this is indeed in good favor with the fire supreme, Gath. The holy symbol has been placed on a golden necklace which goes around the neck of its wearer.