They are lots of fun, and you can find them scattered around the world, here and there.
I have one at Kick the Can Main Store right inside the door.
From time to time, I change the prize in the chair, and I just changed it.
From now until I change it again, if you sit in the chair when it's showing your letter, you'll receive a Treasure Chest. It's not big, and it's not bitsy. It's just the right size to hold a kid's treasures!
It's made of rough wood, with ornate iron corner protectors on all the corners, and iron banding, held in place with rivets. On the top is a Celtic knot design, burned into the wood. On the front is a plain brass latch, with a loop to put your lock into.
When you touch the chest, it opens to reveal a green interior with gold stars; but only if you are the Owner. Otherwise, it does nothing.
It's Modifiable, so you can put your treasures inside as actual prims. If you have mod/transfer privileges on them, you can even link them, so you can carry your box around, or move it from one shelf in your room to another, or tuck it under your bed, or take it into your Inventory, or whatever you like. When you pull it out and open it, your treasures will be intact. (There are full instructions in the Chest Contents, that tell you how to do this and other things.)
It's also Transferable, so you can tuck something special inside, in the contents, or as Prims, or both, and give it to someone you love.
However, you can't buy it. I hope to have other treasure chests; but this one will never be for sale. You can only get it from this Lucky Chair, and only until I replace it with something else.
So come soon, and try your luck!