You can start this quest two ways: the main one is to talk to the women first but requires facing all the monsters. The second way is to find the hidden entrance in which case you'll only face the main monster.
To start the main way, head to the cave southeast of Kaer Trolde Harbor to find two women just outside it and, on spotting Geralt, will call you over. Talk to them to learn they wish to cut the toenails and fingernails of the dead inside as that's the material used to build the mythological ship, the Naglfar. However, the crypt is haunted by wraiths, preventing them from entering.
Agree to help them then head into the crypt. The first floor is void of threats, but the first room down the stairs contains a single wraith. Once killed, head to the next room which has two waiting wraiths, then finally head down the stairs to deal with the remaining two wraiths. Note that the body here also contains Daystar. You'll also notice a destroyable rock wall that leads you through a long, twisting tunnel and out an unmarked entrance just outside Kaer Trolde's gate.
However, you'll notice the objective to kill all the monsters hasn't gone away. Turn back and backtrack to leave and near the stairs that go up to the first floor a nightwraith appears. Kill her to complete the objective. You can then head back out to let the women know the threats are dealt with, earning 50 and completing the quest.
If you instead find the hidden entrance first and enter the crypt that way, you'll only face the nightwraith as you near the flight of stairs out of the flooded room. You can proceed all the way back up and, on exiting the crypt, one woman will cry out in surprise, thinking you're a ghost. Their conversation is pretty much the same other than Geralt informing them he already dealt with the wraiths, earning 50 and completing the quest.
- If Geralt talks to the women first:
- Geralt was surprised to find a group of women hanging around outside the entrance to a crypt on the isle of Ard Skellig - but not as surprised as they were to see a witcher. The women explained they had come to clip the nails of the dead, thus depriving wraiths of shipbuilding material. Though wary Geralt might take advantage to the opportunity to loot some grave goods, they asked him to drive off the ghosts keeping them from entering the crypt.
- Geralt knew the women's actions would do little to keep the Naglfar at bay, but still did as they asked and cleared the crypt of ghosts.
No objectives appear if you used the hidden entrance to deal with the nightwraith.
- Enter the tomb.
- Kill the monsters on the lower level of the tomb.
- Talk to the woman waiting outside.