The Dusty Reliquary is located in the lodge structure located at the top of the hill towards the north end of of the village. It's located in the SE corner of the building, so you'll be able to see it from the entrance.

The village is populated by Tortured Druids (lvl 54-55) and Tortured Sentinels (lvl 56-57). These guys are all single pulls and don't have any special attacks. In the lodge, 1 druid guards the door, 2 sentinels are inside the lodge, and a 3rd sentinel stands out on the east balcony. The balcony sentinel is close enough to aggro when you open the reliquary, so you'll probably have to kill her, too.

The mobs themselves aren't hard, but each one you kill a chance to spawn 1-3 wasps on death. I got no wasps about half the time and typically 1 the rest. I think out of ~20 kills, I may have pulled 2 wasps three times and 3 wasps once. The wasps hit harder than the spirit mobs, so it's nice to have a group for this.

If you solo it (as I did as a level 58 mage), here are some tips that might save you a few fights.

First, there appears to be shortcut into the village from the east side. The lodge balcony overlooks a cliff, but the outer stone wall has a broken path leading down to the valley floor. I did not walk all the way down it since there were sentinels I could aggro below and I'd already fought my way in from the main west entrance. However, I walked sufficiently far down that path that I think it likely that you could use to get up to the east side of the village. As such, it might be worth your while to circle the village until you get to the east side.

When at the east side of the lodge, DO NOT attack the balcony sentinel if you're not on the balcony. She won't jump over the railing, but will instead run through the building and around the outside to get to you. In so doing, she'll aggro the other three mobs on the way, which makes for a lot of potential wasps.

To attack her on the balcony, circle from the east side to the north side of the balcony. You can climb up the rock outcroppings to the north and then jump south onto a stone ledge (the top of the lodge's foundation) that runs around the edge of the building. From there you'll be able to run back around to the balcony and climb over the railing to attack the balcony sentinel. You then have to kill the sentinel closest to the balcony. With those two down, you can open the reliquary without agrroing the the sentinel at the west end of the building as well as the druid in the doorway.

As a mage, here's a way to avoid the fight altogether. Jump up to the stone ledge. Run around to the balcony. You'll aggro the sentinel on the balcony. Run far enough inside to aggro the sentinel on the east side of tbe building. Run back onto the balcony. When you've got the both out there, Frost Nova them in place. Run over to the Relquary and shift+right-click it to open and automatically collect the reliquary. You have enough time to pick up the item before the Nova breaks. Run back to the balcony, ignore the mobs, and jump off the east side. Head towards the stone path. If you run about midway down it and don't attack pursuers, you'll escape their chase range. They'll most of the way to you, but should turn around and head before they close to melee range. At that point, you can mount up and leave however you choose. Much simpler than fighting them head-on.

Toabo's postings are correct as for the location of the reliquary.
It's located in the lodge up the slope on your left side as you enter through the main gate.
I soloed this without problem as a 59 druid and only killing one druid and one sentinel.
I used cat form and stealthed throgh the main gate and up the slope till the rocks sorrounding the lodge.
Walked up the rocks and surrounded the building till i found the balcony.
I regained my elf-form and jumped on the stone basement walking towards the balcony to aggro the sentinel on it.
I killed her and wasp spawned.
While on the balcone just killa the other druid inside in the middle of the room and that's it.
When I killed him no wasp spawned and the reliquary was just in the left corner (if u stand on ther balcony and look inside u can easily loot it without entering)

The whole chain is simple, starts with Rabine Saturna who tells you to go to Silithus get Dusty Reliquary, return to Moonglade to Rabine Saturna, get 2nd part of quest (Shards of Felwine (Quest #5526) ), go to East wing of Dire Maul, loot ground spawn behind the boss Alzzin the Wildshaper, combine box, return to Moonglade and choose reward from Milli's shield (Item #18535) or Milli's Lexicon (Item #18536) a side note, if you go to DM without this quest, you were on 3/22 able to pick up the ground spawn nevertheless and just skip few parts of the quest and running back and forth. After picking up, ran to get the box from Silithus and returned it all to Moonglade. Didn't combine on the way though, so got 2 minor reputation increases (from getting dusty box and from combining and returning 2nd part) to Cenarion Circle. Probably 10% towards friendly, if not a bit less.

Edited, Wed Mar 23 04:15:51 2005

I am level 58 now and Rabine Saturna does not have this quest for me. I found this on http://www.wowwiki.com

Pre-Requisites
The player must have entered Dire Maul at least once.

Source: http://www.wowwiki.com/Quest:A_Reliquary_of_Purity#Pre-Requisites

My Comment is still correct. You NEED to have been to Dire Maul, not necessarily IN the instance but only discover Dire Maul.

(Did this on my Paladin this time)
I took 1 quest from Rabine Saturna called Wasteland when i was level 56 and i had no other quest from him. Went to DM, did the Wasteland quest chain (3) went back to Rabine Saturna for the turn in and had this option that i didn't have before. After i spoke to him i could take this quest: Reliquary of Purity.

The Dusty Reliquary is located in the lodge structure located at the top of the hill towards the north end of of the village. It's located in the SE corner of the building, so you'll be able to see it from the entrance.

The village is populated by Tortured Druids (lvl 54-55) and Tortured Sentinels (lvl 56-57). These guys are all single pulls and don't have any special attacks. In the lodge, 1 druid guards the door, 2 sentinels are inside the lodge, and a 3rd sentinel stands out on the east balcony. The balcony sentinel is close enough to aggro when you open the reliquary, so you'll probably have to kill her, too.

The mobs themselves aren't hard, but each one you kill a chance to spawn 1-3 wasps on death. I got no wasps about half the time and typically 1 the rest. I think out of ~20 kills, I may have pulled 2 wasps three times and 3 wasps once. The wasps hit harder than the spirit mobs, so it's nice to have a group for this.

If you solo it (as I did as a level 58 mage), here are some tips that might save you a few fights.

First, there appears to be shortcut into the village from the east side. The lodge balcony overlooks a cliff, but the outer stone wall has a broken path leading down to the valley floor. I did not walk all the way down it since there were sentinels I could aggro below and I'd already fought my way in from the main west entrance. However, I walked sufficiently far down that path that I think it likely that you could use to get up to the east side of the village. As such, it might be worth your while to circle the village until you get to the east side.

When at the east side of the lodge, DO NOT attack the balcony sentinel if you're not on the balcony. She won't jump over the railing, but will instead run through the building and around the outside to get to you. In so doing, she'll aggro the other three mobs on the way, which makes for a lot of potential wasps.

To attack her on the balcony, circle from the east side to the north side of the balcony. You can climb up the rock outcroppings to the north and then jump south onto a stone ledge (the top of the lodge's foundation) that runs around the edge of the building. From there you'll be able to run back around to the balcony and climb over the railing to attack the balcony sentinel. You then have to kill the sentinel closest to the balcony. With those two down, you can open the reliquary without agrroing the the sentinel at the west end of the building as well as the druid in the doorway.

As a mage, here's a way to avoid the fight altogether. Jump up to the stone ledge. Run around to the balcony. You'll aggro the sentinel on the balcony. Run far enough inside to aggro the sentinel on the east side of tbe building. Run back onto the balcony. When you've got the both out there, Frost Nova them in place. Run over to the Relquary and shift+right-click it to open and automatically collect the reliquary. You have enough time to pick up the item before the Nova breaks. Run back to the balcony, ignore the mobs, and jump off the east side. Head towards the stone path. If you run about midway down it and don't attack pursuers, you'll escape their chase range. They'll most of the way to you, but should turn around and head before they close to melee range. At that point, you can mount up and leave however you choose. Much simpler than fighting them head-on.

As of Patch 2.0 (05DEC2006):

Cenarian Circle rep = 250 for bringing the Reliquary of Purity to Rabine
Cenarian Circle rep = 350 for Shards of the Felvine (combining the shard with the Reliquary)