To the Watery Grave | 5e Adventure Ideas

December 08, 2023
Posted by Luke Hart

By Dean Rigdon

Do you sometimes find it challenging to think up the next big adventure for your 5e campaign? Let us help with these five free 5e adventure ideas!

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To the Watery Grave

Themed around aquatic creatures and environments, these adventure ideas focus on water and its importance to life, as well as the habitats it provides. These ideas span from ancient creatures of the deep to the humble merfolk and weave each creature into the story and location.

Tier One (Levels 1-4)

Dinosaur in the Sea

Creatures. This adventure features the following creatures: bandit, bandit captain, plesiosaurus.

Premise. A plesiosaurus has taken to hunting ships on the coast. No more than an animal, the plesiosaurus is just feeding itself and its calf. Problematically for sailors in the area, they are food for the creatures. The shipmaster’s guild has put up a bounty for the rogue dinosaur, but none are willing to hunt the creature in its lair, for it lies in the territory of a group of fearsome pirates (bandits) and their dread captain (bandit captain).

Plot Hook. A bounty is posted by the shipmaster's guild, offering a large sum of gold as well as free docking anywhere along the rescued coast.

Hidden in Plain Sight

Creatures. This adventure features the following creatures: kelp demon*, merfolk.

*Located in Maritime & Madness, Lair Magazine #24, December 2022

Premise. Children have been going missing in the night in a merfolk village, close to the coast. The merfolk are convinced that it is a kelp demon, a tall tale coming true. However, the true villain is the merfolk in charge of the village, whipping the mer-people into a frenzy to cover up their illicit dealings. The frenzy has reached a point where many have fled the village, backfiring on the village leaders. They now need proof that the “demon” is dead to convince the merfolk to come back.

Plot Hook. The leaders of the merfolk village put out warrants for the kelp demon. In secret, they call adventurers to their private chambers and ask them to bring back anything resembling a kelp demon, to quell public fears. They offer, in return, the locations of treasures lost at sea.

Tier Two (Levels 5-10)

Five Problems

Creatures. This adventure features the following creatures: hydra.

Premise. A hydra has followed underground sewers to an unfortunate location in a large city, the central water spring. The entire city is supplied by the massive fountain and pool, full of fresh water. The city now has numbered days before water supplies run out and the entire city dies of dehydration. There are several other locations to get water, but none can fully support the city. The hydra must be thwarted, or much of the city will perish.

Plot Hook. The leader of the city is actively looking for adventurers to brave the spring area, putting out bounties, calling in favors, and doing everything to keep the common folk from dying. The leader isn’t sympathetic necessarily, but if the workers die, so does the city. The city leader is offering many thousands of gold pieces and declares that they will forever be indebted to those who help the city.

Tier Three (Levels 11-16)

A Nation at War

Creatures. This adventure features the following creatures: aboleth, giant shark, merfolk.

Premise. A devious aboleth has started to enslave village after village of merfolk. The merfolk do the aboleth’s bidding and ride enslaved giant sharks to do battle with ships that cross the oceans and seas in the aboleth’s territory. Many coastal cities have been cut off from the sea, resorting to slow land transportation. The affected nation has declared war on the aboleth, and the entire country now prepares.

Plot Hook. Nations are looking for mercenaries to supplement their troops. They need trained fighters, not commoners with swords. These mercenaries are given special tasks, and some well-known mercenaries are even called to talk with the nation's empress personally. She offers honor and prestige, land for all who assist, as well as a healthy sum of gold.

Tier Four (Levels 17-20)

A World of Wet

Creatures. This adventure features the following creatures: cultist, cult fanatic, kraken.

Premise. Deep beneath the water lurks a kraken, slowly building its following of cultists and fanatics. Members of the kraken’s cult have infiltrated the high courts and confidences of every ruler in the world. The cultists are setting up portals connected to these depths where the kraken resides, allowing the kraken to emerge and strike anywhere it chooses. Nations will fall like dominoes; the kraken must be stopped, or the world may be irreparably damaged.

Plot Hook. Cultists have been captured by several different nations, who have started to uncover this masterful plot. Unsure of who they can trust, they call upon the noblest heroes in the land to help them uncover the true nature of this devious plot. They offer a powerful magical item to the heroes of legend, hoping that it will help them in their quest.