Here's something rather natty. Some clever sort has created a thing called Daggerfall Tools for Unity. They describe it as "a code asset which acts as a bridge between Daggerfall's binary data files and Unity3D."
What this essentially seems to mean is that if you own a copy of Daggerfall - which Bethesda offer as a free download, bless 'em - you can use Daggerfall Tools to import all manner of assets and content into Unity projects and then tinker as you like.
The list of features the tools include is dreamy: enemies come pre-loaded with animations, there are custom components to handle stuff like switches and doors, many of the GameObjects created during the import process come with useful metadata... why, take a look for yourself.
What you've got here is a big old game development sandbox based on one of the most famously sandboxey game series of them all.
Here's developer Gavin 'Interkarma' Clayton on these tools:
Daggerfall Tools for Unity is a code asset which acts as a bridge between Daggerfall’s binary data files and Unity3D. It consists of a mature API for opening and converting almost all of Daggerfall’s content files – plus a set of editor windows, example classes, and prefabs for quickly converting Daggerfall’s environments into fully functional Unity scenes.
The underlying API, called DaggerfallConnect, is a battle-tested C# library that has been under development since 2009. This library is already used by content exploring tools with thousands of downloads and has been retooled specifically for use inside Unity. Full source code is included for everything related to Daggerfall.
Accompanying the API is a suite of components and editor windows to interface between Daggerfall’s files and Unity. You can import any mesh, block layout, city, building interior, or dungeon with a single click. There are dozens of options to control how content is imported into Unity, using either the editor or directly from code.
Everything you can import with the editor can also be imported fully procedurally at run-time, allowing you to build vast worlds out of Daggerfall’s content and extend however you like with Unity’s broad feature-set.
I literally could not have put it better myself. I'm no developer, but I have enjoyed fiddling about with Unity. I've made a few tutorial projects, a game level in which you walked towards a sphere that made noises at you, and - hat tip Kerry Turner - a rather nice tree. To this list I think I might add "making a tremendous, glorious mess out of something beautiful".
(Unfamiliar with Daggerfall? Here's a lovely article from the archives, contrasting its design ethos with that of Dark Souls.)