Warning: Do not stray from the path! The lava here will kill you very, very quickly, and the cliffs do not have invisible walls. In other words, the only Ouch!! you will get when moving off the edge of the cliff is the one when you hit the bottom and die.
From the beginning point, in the center of the first square:
N S S E S W N E
Answer the first riddle. Answer is
After the first magic mouth, proceed:
Answer the second riddle:
After the second magic mouth, proceed:
S E W W E S E
Then follow the narrow path (see warning above) over a few lava pits. Use Restoration as needed. You will have to fight two fixed battles before reaching the Dragon's Grave.
First fight 25 Fire Guardians.
Second fight is 25 Bogeymen. They are more dangerous.
This is an easy fight if you have been through Inferno. Just use Close Combat to bring them into melee range.
Cross the final stretch of lava and open the Dragon Grave. I used two charges of a Dietrich and my rogue's lock pick skills. Once you have the egg, exit through the last bit of lava to the east. Carry the egg back to:
Use Close Combat and Hesitation.
If you are in the expansion, the dragon egg will hatch and the baby dragon will offer to join your party. It will wait patiently for you to travel to camp in Castle Cranbourgh, dump a character, and come back. You need the baby dragon to:
The previously locked door in the far SE corner of the basement of the Castle Tower (aka Abandoned Tower) south of Castle Cranbourgh.
If you have not bought the expansion yet, why not?? But until you do, you can wander around gaining XP, and visit the dragon egg anytime you want.
Enter the Gateway to the Planes. Once you have done that, you can dump it by visiting a camp (where you can pick up your seventh character again) or by taking the road wardens, who do not accept non-player characters.
By the way, like all wandering creatures, the dragon will occasionally turn on you. Keep an eye on its mood and cast Camaraderie as needed to calm it down.