Did you talk to Jedediah, the guy walking around by the hatch? He tells you what you need to get the crypt open. If you have the chalice (from the slayer camp near the harbour), you just need some Drudanae, which can be gotten in High Hall.
You need to deal with the troll problem in High Hall first. After that, you can buy some Drudanae from the merchant, or mindread him, enter his house and find a secret passage to where he is growing it.
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