To get the Rusty Key, you’ll need to find and donate 60 items to the museum. It may seem like a lot, but there are 95 items to find in total—so it can be done! If you’re not sure whether an item can be donated, check its description in your inventory. It’ll say, “Gunther can tell you more about this if you donate it to the museum. "
Potential artifacts you’ll find this way include fossils, anchors, and ancient or prehistoric items like dolls, instruments, jewelry, and weapons. You’ll need to dig artifacts up with a hoe, as other tools won’t work.
Keep in mind that the mines are inaccessible until the 5th day of Spring (Year 1). You’ll get a letter informing you when you can visit the mines. The mines are large, containing 120 levels total with increasingly valuable ore on each descending level. To get to the next level, find a ladder somewhere on your current level of the mines.
In addition to ore and gems, you’ll also be able to locate artifacts by fighting dinosaurs on the prehistoric floors of the cavern.
For example, defeating monsters is the only way to get the game’s Dwarf Scroll collection, unlike other artifacts. To slay monsters, make sure your character has a weapon (especially an enchanted weapon), food items that give buffs, and good mobility. Time your weapon strikes so you can push away or damage monsters effectively.
In Stardew Valley, fishing spots are ranked from zone 0 to zone 5 (5 being the best zone). The further away from land in every direction, the better the zone. A zone 5 space is at least 5 tiles away from land.
Conversely, when the spirits are “somewhat annoyed,” “mildly perturbed,” or “very displeased,” you’re less likely to find special treasures in the game.
You may also collect bone fragments from a node, which is useful because they can be used in crafting, and Gunther will make a special order for you to collect 100 fragments at some point.
There’s no need to donate all the items simultaneously, especially since you have limited inventory space. Donate to the museum during its open hours (8 AM to 6 PM) as often as you want.
