A cave can be beautiful, but is not very useful to most people, maybe shelter, but little more. Caves often contain water, some are flooded, and even freeze in winter. But due to a combination of favourable conditions, only one is known to actually stay frozen, even in the hottest of summers!
After discovery, it was a nice curiosity for a few years, if ignored otherwise. Kids often played there on hot summer days. Then, a little girl came back to her camp with fresh strawberries in her hand. But it was late autumn, and no strawberries grew anywhere! The puzzled elders soon got their answer, and the very next year the cave has seen its use…
The primitive hunters and gatherers have their good and bad times. In summer, where everything grows, and game abounds, it is good to become fat. The seasonal migrations are an excellent source of much meat, though it is better consumed fast, as ways to preserve it are limited.
Winter is the season when you become lean and often hunger. Anything left from the better months is good. No wonder a big natural refrigerator has become such a hit!
You can set the present at whatever moment you want. Maybe the tribe was just recently began to use the cave, and wants to keep it secret. A large part of its provisions is hidden there, and other tribes would surely take it with the idea.
Somewhat later, the secret is inevitably out, and the cave is guarded all the time, or sealed and masked to stay hidden. The tribe will have to stay in the area, and keep an eye open. Anyone seeking hidden underground locations will be instantly suspicious. Or if someone has a map leading to this cave, a few centuries old? Trouble and heated arguments guaranteed.
Later, the cave may serve as a food-bank for numerous tribes living nearby. A hotbed of tribal politics will be born, be sure to visit it. Some larger or more numerous humanoids may also want the cave for themselves, and take it without asking.
And still later? While it may be definitely exaggerated, a single cave may be the start of a new nation. Giving more time to create new inventions, forcing a tribe always on the move to settle, and creating alliances… who knows? It may become a memorial of how things started long ago.
At any point, some ice could melt, and something could be found inside. Whether a cute fuzzy creature, that can threaten the ecosystem one day, or some magical beast that should have stayed imprisoned? Or perhaps some strange disease from aeons ago? (remember X-files)