In the Ice Cave

Perched high on the cliffside lies the lair of the young white dragon. Nearly inaccessible, it can be reached by recklessly scaling the cliff, or by air.
The cliff rises about 300 feet from the valley floor. The cave entrance is on a thin ledge of ice 100 feet from the top of the cliff. Using ropes and spikes or grappling hooks, the party can make the climb in roughly four stages, basically 50 feet per stage. As long as they are using ropes, they should be able to make the climb without fear of falling. This is a difficult climb, so it requires a successful DC18 Athletics check for each stage of the ascent.
The party should make a group check for success. Each member of the party making the attempt at the climb rolls against the DC18, with a majority of success or failure determining the result. As long as the party are using ropes, failure will only mean an extra stage of climbing. If all members fail by greater than 5, have them slip down 50 feet. If the climb takes more than 6 stages to make the ledge, the dragon will come out on the ledge, having sensed danger, and coming to investigate.
If the dragon emerges, it will fly out to use its breath weapon on the exposed characters. Their best option will be to finish the climb, and try entering the dragon's cave, forcing it to reenter in order to get to them. If the party is able to reach the ledge and enter the cave before the dragon emerges, they will find it at rest, hanging from a perch on the far side of an enormous ice cavern.
The cavern is 100 feet across, and coated with ice, making it difficult terrain to cross. The entrance to the cave is 20 feet above the floor of the cavern, and the ceiling rises 60 feet above the entrance ledge. The dragon can be seen perched on a ledge 10 feet from the ceiling on the far side of the chamber, where it appears to be resting. Once any movement is made within the chamber, the dragon becomes aware of the party's presence.
Unlike the cliff face outside, the chamber is full of small ledges and broken surfaces, making it possible to cross and climb without the use of ropes. The ice makes the surface of the cavern difficult terrain, but characters can attempt to move their normal speed with a successful DC15 Athletics or Acrobatics check. The floor of the cave is scattered with small elevation changes, and stalagmites which can provide partial cover for line of sight spells and targeting. The dragon's breath weapon is a cone of icy breath, which ignores any such cover. Within the ice covering the floor and small platforms are sparkling gems and occasional glints of steel.
The dragon will remain up high, and try breathing as often as its breath weapon recharges. On turns where it doesn't, it will swoop down to attack with its bite and claws, then move away to a spot high on the wall. This is a young white dragon just establishing its lair. As such, it does not exert any regional effects as a more established dragon might. It does have the ability to use lair actions of initiative count 20 as listed in the Monster Manual.
For treasure, there are 800 cp, 6000 sp, 2600 gp, an 140 pp. In addition, there are 11 gems worth 100 gp each, and three magic items - two +2 weapons, and a wand of paralysis. The treasure will be scattered throughout the cave, mostly encased in ice. Once the dragon is dead, the temperature in the cave will gradually rise, although it is likely to take days to fully return to a natural state. Much of the ice has been created by the dragon using its breath weapon to create an environment preferable for its taste. If the party is willing to spend a full day recovering the treasure, allow them to uncover it all. Otherwise, reduce the amount of coins by 10-20 percent to allow for haste.