Fight your way through the Oratorium (level 50-51^^ giants) to Flame Lord Thyr.
Hail him to spawn two Efreeti minions. Any member of the party can do this, as long as the party is prepared to fight the Efreeti after the hail.
Tip: You must be close to him to get the conversation tree - Target Him and press H.
After defeating the Efreeti minions, have a non-critical party member hail the Flame Lord.
The person hailing the Flame Lord is temporarily banished to a cage from which they cannot escape and will draw aggro from magma elementals in the zone (if they haven't been cleared previously). Note: even if the magma elementals do not aggro (ex: they are grey con) you will need to fight them anyway once banished to the cage.
The person doing the hailing should obviously not be your main tank. Conjurers, Necromancers and Illusionists are able to use their pet while in the cage. It is also possible for some classes to cast down on the Flamelord and to heal from the cage.
If you can solo the Flamelord, it is possible to range pull him to the cage (or root him to a safe distance) and complete the instance solo. If you have trouble ranged pulling the Flamelord, you might try using a pet (tinkered, or other) to pull him to you.
After the Flame Lord is defeated, the person in the cage is immediately teleported to the back door from the cage.
Go through the Back Door, down a short stairway and ring the Gong to get to Nagy
Once this instance has been cleared once, you can bypass the content to go further in by zoning into the Oratorium of Thyr (Deserted). You can then choose whichever of the instances you want. Advisement: When returning to this instance, do not have any mercenaries summoned before zoning in, or you will be placed in the uncleared version.