Hawke's Estate becomes available to the player right after the conclusion of the First Act of the game (in other words, after the Deep Roads Expedition). The Estate is basically a replacement for Gamlen's home from Act 1, and is mostly significant for allowing you to receive more quests from letters on your writing desk. The Estate is located in Hightown, and can be visited directly from the World Map once you visit it once.

It is best to visit it right after the Deep Roads Expedition to catch up on quests as well as the story. Afterwards, you can visit it quite often to receive new letter quests.