G1-2-3: Against the Giants
Against the Giants is one of the oldest Adventure Paths for Dungeons & Dragons, if not the oldest. It consists of three modules, also known as the "G Trinity" for their official coding (G1-G3), which are individually named Steading of the Hill Giant Chief, Glacial Rift of the Frost Giant Jarl, and Hall of the Fire Giant King. They were originally published in 1978 for Advanced Dungeons & Dragons 1st edition, but were reprinted in a collected format in 1981, which is when it gained the title that we use here. As the name suggests, it revolves around the party being called upon to fight giants.
Against the Giants canonically forms part of a greater Adventure Path when linked to the Drow Trilogy, which in turn is linked to the module Queen of the Demonweb Pits. The entire adventure path was released in a super-omnibus form as the first part of 1986's Queen of the Spiders, then in 1999 Sean Reynolds re-rereleased the path for 2e in Against the Giants: The Liberation of Geoff but oriented away from the Underdark.
G1 Steading of the Hill Giant Chief
The module begins with a prologue explaining that giants of different types have been raiding lands occupied by humans. Angered by this, the human rulers hire a group of adventurers (the player characters) to "punish the miscreant giants." The players' party is informed that they must defeat the giants, or have their heads placed on the chopping block. The human nobles equip the party with weapons and horses, along with a guide and a map that shows the location of the hill giants. The players are informed that the hill giants are led by Nosnra, a sly hill giant chieftain who loves to set up ambushes; there is an unknown force binding together different giant groups. The player characters are informed that they may keep any spoils they find, but must return at once if they determine what "sinister hand" is behind the alliance.
The bulk of the adventure takes place in two locations: the upper level fortress of the hill giants' lair, and the dungeon level beneath it. In the upper level there are halls, barracks and common rooms. These rooms house Chief Nosnra and other hill giants, ogres, and servants. The dungeon level consists of slave quarters, torture chambers, and caverns. These house troglodytes, bugbears, and carrion crawlers. The majority of the treasure can be found by searching the dungeons. The chief's treasure room contains a map of the glacial rift from Glacial Rift of the Frost Giant Jarl, and a magic chain that automatically transports the party there.
G2 Glacial Rift of the Frost Giant Jarl
This module starts in one of two ways. If the players have finished Steading of the Hill Giant Chief, they have been transported to the glacial rift via the magic chain. They will know that they are searching for some force behind the giant alliance. If the players are starting with Glacial Rift of the Frost Giant Jarl, then they have been hired by nobles to destroy the frost giants. Either way, a safe, hidden cave is easily found for a base of operations.
As in Steading of the Hill Giant Chief, the bulk of this adventure takes place in two locations: an upper area consisting of caves and the rift floor, and a lower area consisting of natural caverns. In the upper area there are ice caves, barracks, and a dome of ice. These are inhabited by yeti, frost giants, ogres, and winter wolves. The dome of ice houses a remorhaz. In the lower area there are caverns that house the servants, serve as a prison, and contain the Jarl Grugnur and emissaries who have come to meet with him. The main inhabitants are frost giants and ogres. The prison contains an attractive storm giantess. There are also polar bears; pets of the jarl. After defeating the jarl, the adventurers have a chance to pull an iron lever which will transport them near to Snurre's hall from Hall of the Fire Giant King.
G3 Hall of the Fire Giant King
If this module is played as a continuation of the first two modules, the players know that they are searching for the force behind the giants' alliance; otherwise, they have been hired by nobles to destroy the fire giants. This module is twice as long as the previous two: sixteen pages instead of eight. Unlike the two previous modules where the giant's complex consists of two levels, the fire giant hall contains three levels. The giants live in a hot, smoky barren area made of rock; as in the previous module, the party is able to find a safe location for forays against the giants. The leader of the fire giants is King Snurre Iron Belly, and his hall is made of obsidian and natural caverns.
The first (top) level includes the queen's rooms, barracks, and kennels. Creatures encountered here include fire giants, gnolls, and in the kennels, hell hounds. The second level is also made of obsidian rocks and natural caverns. It houses chambers of spiritual interest to the fire giants. There is a hall that houses the dead fire giant kings, and rooms for worship. There are also rooms that contain drow clerics. This is where the party learns that the drow are behind the giant alliance, led by Eclavdra, a high level drow fighter/cleric. The third level consists of natural caverns and contains a great treasure guarded by a red dragon. There are also more fire giants and drow; to exterminate the fire giants, the adventurers must penetrate deep into the active volcano where they live. If the DM wishes, there is a tunnel that leads deep into the earth; to the home of the drow. This allows the adventure to be continued in Descent into the Depths of the Earth.
G4-6: The Liberation of Geoff
As noted, Reynolds' rework had the intent of treating this giant-focused series, as a giant-focused series; refusing to chase that dark fey SQUIRREL down into the depths. Unlike with Scourge of the Slavelords this time Reynolds left the G1-3 well-enough alone - so, yeah, the drow agents are still here. But this time the party is supposed to back away from the caves, and head north instead.
G4 is Mount Rungirheim, another frost-giant lair. G5 is Castle Thrasmotnir, for fire-giants. In between the expansions concerning occupied Sterich in the Queen of the Spiders supermodule are taken to a higher level here in Geoff.
G6 is the final battle, a cloud-giant lair. The whole invasion was set in motion by the Sakhut. The Sakhut hail from the far west and speak a Baklunish language. They view other giants as their natural serfs, and man-sized humanoids as edible monkeys.
4e also directly converted the Against the Giants adventures, adding both a new interquel adventure "Warrens of the Stone Giant Thane" between Steading and Glacial Rift and an optional sequel, "Unfriendly Skies", in its run of Dungeon Magazine. The Giants quadrilogy ran from issue #197 to #200, whilst Unfriendly Skies appeared in issue #205.