Lythia.com is the site to download various fan created items for Harn and Harnmaster and it all free to the download. Some items are specific to the world of Harn while other are generic and can be used in any fantasy medieval campaign using your favorite set of rules.
This is a scanned handdrawn alternate set of floorplans for Gythrun castle in the Kingdom of Melderyn. However the article is just floor plans so you can use it as a generic castle in your campaign.
Geology of Harn
A fan with a good knowledge of Geology comes up with a consistent of why Harn's landscape is the way it is. It does some use in a fantasy campaign as it shows how the underlying geology can impact who and what is found in a area.
Maps and Locations
Maps of a hideout, tavern, and a weaponcrafter shop. Useful for any fantasy campaign.
A small village in the Kingdom of Kaldor. With a small amount of work can be used in any fantasy campaign. It also part of a project to completely detail Nelafayn Hundred in the Kingdom of Kaldor.
A hundred is a territorial subdivision of a shire. In England it represented land worth a hundred hides enough to sustain a 100 households.
You can download a free Harn Map Key from RPGNow.