"The Keep in the darkness" was a multi-leveled adventure a Dungeon Master I used to play under made. It started like most Dungeons & Dragons games with everyone meeting and partying up in a city circa the 'Tavern'. It was a ever changing mission which started the group with simply boarding and fighting their way through 4 levels of a pirate airship, to find and defeat the 'main boss' only to find out he was working in conjuncture with Duregar Dwarves to undermine the friendship of the local Dwarves with the other races.
We then had to find our way down to the evil Dwarves city which was 6 levels filled with angry evil Dwarves, pits, traps, a full labyrinth with Displacer Beasts and other baddies chasing us every wrong move we made. We get to the bottom level only to find the core leadership of the Duregar taking a teleportation trip to where? A Drow city readying for an assault on a major Elvin nation.
After two days wait, and scrounging for restocking goods and arsenal, our group's wizard found how to recreate the teleport spell, and we were on our way again. An all out dash past the army,and a brawl up 5 levels of the Drow Queens keep, we find the woman and the Duregar group stepping through another portal.
We find our way through the portal with the help of an unhelpful Drow's severed hand and her 'pure blood'. The game ended with us having to stop the Duregar and the Drow from attacking the Elven nation. The attack was to be proceeded by the inactive volcano deep in the Elven nation, to be made Active and blow. The battle started underground where the Duregar set magic and explosives to restart the volcano from just below it. They lit it, and it became a race up through the top of the volcano to catch the Duregar caster and the Drow Queen and her personal guards. The fight ended at the top of the volcano where scouts in a nearby tower of the Elven Nation saw the battle, and a contingent of the nation came to our aide just after we had lost about a third of our party in the fight when the Drow Queen summoned a demon to her aid.
The Duregar caster, the Demon, and the Drow Queen were all defeated by the end, and the Elven nation stopped the volcano with several Casters making 'create water' down the spout, and then imploding the volcano into itself from the middle.
This was the main parts of the mod, but with the fluff it took almost a year of Saturdays to complete. Afterwards, the group started a new mission in a city at a 'tavern'.