Journey to the Ygg
Journey to the Ygg is a one-shot idea for winter. It is planned for 4-6 adventurers of 8th level.
Background Lore
In time long past, the 3 nations warred endlessly. Arctus, Lycos, and Chelona (árktos, lýkos, and chelóna, Greek for Bear, Wolf, and Turtle, Αρκτος, λύκος and χελώνα) were at war.
Arctus is the land of humanity and it's offshoots (halflings, changelings, tieflings, etc.) it is a cold, northern climate with boreal trees.
Lycos is the home of the more bestial races (lizardfolk, tabaxi, kenku, aaracokra, etc.) a rainforest on the western coast gives way to mountains, causing a desert in the rainshadow.
Chelona was the home of the long-lived races (elves, dwarves, gnomes, etc.) with rolling hills and thick woods. While some of their descendants still live, none have heard from their ancestral home in many years.
The Arch-Trees
A powerful druid -- some believe her to have been a goddess -- sought to put an end to the wars by giving them something to rally against. To this end, she began a dark ritual, summoning great monstrosities in the depths of the world. These monsters would filter out of the caverns, attacking the peoples of all 3 nations. In a show of her purpose, she broadcasted a message.
"Because you could not find peace amongst yourselves, you and your children shall never know peace. These beasts will continue to ravage your lands, unless you learn cooperation. A great tree grows in the north of your lands. You must make an offering to this tree each year, or the beasts will grow stronger, your crops will fail, your lives will be forfeit.
"These trees. Ygg in Arctus, Dra in Lycos, and Sil in Chelona, will be your protectors. Care for them, offer tribute, and you will continue to survive."
Chelona, the ageless elves in their woodland sanctuaries, the dwarves thinking themselves invincible in their mountain homes. Their pride was their downfall. Only a few years passed, and their tree fell.
The Ritual
The ritual varies for each tree. For Ygg, it requires a white hare, a bronze brazier, firewood, 1lb of Chestnuts, and several mistletoe berries.
A fire is started in the brazier, which the chestnuts are placed on the rim of the brazier. You then feed the hare the mistletoe berries before dropping the animal into the fire. The hare will leap out of the fire unharmed (the poison from the mistletoe is magically neutralized) and the fire will turn green and start spreading. Once the green flame makes contact with the Ygg, magical energy surges up the tree. The fire will extinguish itself, and the Ygg's branches will rapidly show new growth, it's roots tightening around the caverns that allow the monstrosities to escape. Finally, the tree will drop its seedpods onto the monstrosities nearby, killing them or driving them away.
Life in Arctus
It has been 1000 years since these events. For Arctus and Lycos, this has become a fact of life. Make tribute, and the wilds will remain peaceful, game will be plentiful, rain will fall in it's season.
For all but 12 days of the year, the way to and from the tree is blocked by harsh storms and avalanches. This leaves only a small window for the offering to be made.
Similar happens around Dra, though coarse sand instead of snow.
Plot-hook
In the land of Arctus, each year a pilgrimage is made to The Ygg, the great tree. Without the ceremony and offering, the Tree's roots weaken, allowing greater monstrosities to escape the caverns beneath. You were chosen for your strength, skill, and cunning, to guard the caravan to The Ygg. During the last cycle, the caravan failed, and hard times have come since. No one is sure what happened to the last caravan, but none returned. Many crops failed, game has been scarce, and this winter is looking colder than the years before.
But hard ground makes for stronger roots.
Your mission is, through stealth or strength, to ensure the priest makes it to The Ygg and completes the ceremony. The priest, Erelyn, has seen many cycles. He was retired, with a successor taking the mantle. But with the last year's failure, he has returned from retirement to make the pilgrimage once again.
Enemies
Hydra (final encounter)
Death Dogs
Displacer Beasts
Deep Crow (not meant to be fought, plot device to push them underground)
Young Kruthik
Adult Kruthik
Kruthik Hive Lord
Story Beats
Set off from town
Erelyn gives more information as they travel, as he is experienced.
Confrontation with Death Dogs
A deer runs across the trail. Unnervingly, the deer's thigh sloughs off and falls to the ground in the middle of the road. The deer stumbles and falls, as a wolf pounces on it. A head turns towards the party as the other eats the discarded flesh.
A successful nature or survival check (DC 10) identifies it as a Death Dog. DC12 they are informed of the nature of the diseased bite. DC15 recalls they are afraid of fire, and won't attack anyone holding a torch or other flame. Ranger with Monstrosity focus automatically identifies them and has advantage on the latter 2.
As one head has the group in it's sights, the other howls.
In 2 rounds reinforcements arrive. 2 on round 3, 1 more on round 4, and 3 on round 6.
Death from above
As dusk settles, you hear an echoing "caw" in the distance... Nature or survival DC15 identifies that as a Deep Crow, only heard of in stories. Erelyn recommends getting underground immedietly. Conveniently, there is a 10x10 cave entrance nearby.
The party can make camp at the mouth of the cave for a long rest and continue overland in the morning, or proceed through the caves (see 3.1 below), before or after a rest.
...and below
As they journey deeper into the caves