The third box set for D&D rules this one covers 16 to 30(I think). The focus of this set is PC's setting up there own strongholds and ruling the surrounding areas. I never played a D&D campaign long enough to get to this level but it does add to the first to rule sets. Also I don't think any other rule set covers the topic of high level campaigns as well, sorry players options.
[4 of 5 Stars!]