'I said that I do not know where lies the vault containing Arwen's legacy, but it may be that I can help you to gain entrance when it is found.
'The riddle itself may be the key to the vault. If in your travels near Imladris you find a sealed vault, those words may offer you passage within. There should be a rock in front of the entrance. Place your hand on the rock and recite the verse.
'I would be surprised if the jewel is in the vale of Imladris itself as these carefully tended gardens and groves are too often frequented by the Elves for a vault to be easily hidden. I have no doubt it is close by, somwhere in the Trollshaws not far from Imladris.'
Glorfindel does not know where Arwen's legacy is, but he has given you some advice which may help you to find it.
1. The lost Elf-vault is somewhere in the Trollshaws in the vicinity of Rivendell.
Glorfindel advised you to place a hand on a rock by the entrance of the Elf-vault and to recite the verses of the riddle. Arwen's legacy, a white jewel, should be somewhere in the vault. If you find the jewel, return to Glorfindel with your prize.
2. Elrond is in the library of Rivendell.
Glorfindel asked you to bring Arwen's legacy to Elrond.
There are only a few monsters in the dungeon - 4 crawlers. The last crawler will spawn two helpers when attacked. I found that if you're solo, take out the helpers first.