Titan from Fighting Fantasy, in particlur- Allensia. The party starts off around Solomnias with levels 1-10 doing various FF gamebook-like adventures- Forest of Doom (drow!), City of thieves (Blacksand!), Island of the Lizard King (Lizardmen! A Volcano!), Temple of Terror (Yuan-Ti!), Deathtrap Dungeon (It's a Dungeon!) I'm using some of the 3rd ed module versions that were made. The end of the heroic level will be stopping Bathes Dire in his Citadel of Chaos from invading Allensia (and mabye a sidetrip to vis Zador the Warlork of Firetop Mountain).
Paragon and it's off to to explore the area of Creature of Havok, introduction to Spelljammer (The Galleykeep) and off to spelljamming in the heavens.
I foresee Planscape being 20-30 eventually.