The House of Curios is a very rare instance that spawns in the Fields of Misery zone. The instance itself is located in a named sub-area called the Lonely Dwelling. Finding it will require getting lucky, or spending a lot of time running and re-running the zone. To find it, head to the Fields of Misery, check each of the six possible spawn points and, if you don't find it, leave the game and then resume. Setting your quest right could allow you to enter the game right in this zone, reducing time spent travelling.
There are six chunks in the zone that will each be filled by random tiles. Two of these are always the Waypoint and the Khazra Den, the latter required to move the quest forward. Hence four of the six chunks will be filled out from the other possible tiles. One of the chunks is smaller than the others, and won't fit a large tile (but could fit the Lonely Dwelling or waypoint).
In the following image, I've outlined the six random spots, and labelled them with what they happened to be for me that game. The chunks will be in the same places, but the content inside is random.
The possible large tiles are:
- A "goatman rally," taking place near several burned homes
- A lake
- The Secluded Grove minizone, with a tree-spirit ambush
- The Forsaken Grounds, location of the Carrion Farm event
- The Forlorned Farm, and entrance to Farmer's Cellar
If a tile doesn't have one of the above, it could instead have:
- The Lonely Dwelling, entrance to the House of Curios
- Entrance to the Lost Mine dungeon
- Entrance to the Scavenger's Den dungeon
If a chunk has one of the 'small' bits, the rest of the chunk seems to be filled with other random stuff, such as a burned tree, or an old sawblade. I think the Khazra Den and Waypoint are actually 'small tile' candidates in the game's algorithm. Also, the Burned Tree could be one of the large chunks, but I'm not sure -- I found my House of Curios and haven't researched further. ;) Anyway, point being, there's these six spots, and you should check all six.
Also in this zone, near the top (northernmost) corner of the zone and a bit down and to the right, are a few steps that lead up to a small house. This can be one of three different things: just a decorative house that you can't get into, the Pillaged Home instance, or the Tinker's Hovel which is the location of the Wandering Tinker's Diary.