As you adventure your way through the deep dark caves of Spelunky 2, you will occasional come across a Golden Key. A lifetime of gaming has programmed us to believe that such things are very important, and this is certainly the case in Spelunky 2.
Keys can appear from chests, breaking pots, or you might even come across one just lying on the ground. To bring the key with you, you will need to hold it, which means you can hold anything else until you get rid of it.
Now that you have a key, it is time to find the chest that it will open. These chests cannot be found out in the open, and instead you will need to explore all the small doorways that you can find in the walls of the level. Hitting R1 in front of these doors will bring you inside, and you can find all kinds of things in there, including a very ornate looking chest.
Now it is important to note that these keys and chests go hand in hand. If you find a key, there will be a chest and vice versa. If you do manage to open the chest, it will contain an item called the Udjat Eye. It will reveal hidden gems, so you will know the best place to put your bombs to get plenty of money. It is also one of the items that you need to make your way to the Black Market, although we have no managed to confirm this ourselves yet.