One of the first locked dungeons you will encounter in Solasta: CotM - Lost Valley is locked behind two keys. Here is a quick guide on where and how to find both of them.
Solasta: CotM generally doesn't hold the player's hand and when it comes to finding secrets, someone might get lost along the way. The game will not tell you where to find the two keys needed to open the dungeon in the first map you come across during your adventures in the Lost Valley.
When you stumble upon the dungeon, the entrance will be behind a few Gorillas you need to dispatch and when you do try to open it, the game will tell you need a bronze and a silver beetle key.
The opportunity to get the first key is likely the one in the other locked dungeon in the same map. You can find it between the Forge outpost and the Giant enclave, the entrance on the map will be called Waterfall Grotto.
In order to access the dungeon, you will need to remove the giant rock from the entry point and to do that, you will need someone in your party who speaks giant. Alternatively, you can use Comprehend languages spell and interact with the giant in front of his enclave to engage in a conversation.
Do the giant's bidding until, and including, the objective where he asks for materials to make himself a chair. Once he has everything, he will ask you to find a big flat rock, at which point you can direct him to the one at the cave entrance. He will take the rock and you can enter the cave.
You will need to fight a few low-level enemies inside to get to one set of containers that can contain a key but they shouldn't be a problem. Just make sure you don't climb on the plateau where orc enemies can be found and don't go to the Minotaur Crossing before level five.
You can also loot them in secret places outside of dungeons. For example, you can just follow all the quests you get from the People faction. This will cause you to enrage the Dominion at one point or another but it will potentially lead you to the second key.
Progress the questline until the People invite you to their hideout in the middle city, at which point you can just loot the containers inside and grab the key.
Another place that can yield a key is a dungeon that can be entered from the Swamps after Hasrubdal tells you about a Major Gate.
Rewards in the dungeon are significant but I would suggest levelling to at least seven before entering. Otherwise, the progress might end up slow as you will need rests too frequently and the final fight might end up a nightmare. That said, there is nothing stopping you from entering as soon as you grab the keys.
Either way, good luck and happy hunting.