Legend has it this item was created by a mad wizard to enable him to live in the forest without having to share his space with pesky neighbors, or intruding adventurers. It is also rumored that he was hiding from a secret organization only known as "Them", ans so disguised his home to look like a stump. The truth has been lost to antiquity.
This seemingly normal acorn, is anything but. You conjure an extradimensional dwelling, that looks like a rotten old stump, in range that lasts for as long as you wish. You choose where its one entrance is located, and which direction it faces. The entrance will appear to be a section of stump that has rotted away. You and any creature you designate when you cast the acorn to the ground and chant its activation can enter the extradimensional dwelling.
Once activated, and you enter the stump, it becomes a cozy 3 bedroom home with a living room, stocked kitchen, front room and a library. Items can be taken into the building, and even stored in it for a time. Any other extradimensional spaces are sealed off while within the structure, and will no longer function. Every morning at sunrise the larder is restocked with simple but filling fare, and basic water. The food stuffs and water are enough to feed a party of 8 people indefinitely. The library is filled with a large number of tombs, scrolls, and other knowledge. (The exact information is determined by the game master, and appear to be donations from the previous owners) Furnishings and other objects that are considered part of the stump dissipate into smoke if removed. Other items, or people, left in the stump while in transport can be retrieved as normal once the acorn has been "planted" for use again.
When you place the acorn on the ground, chant it activation phrase, it will turn into the outward appearance of an old broken stump of surpassing normality. The stump is so common and boring that normal people would not even look at it. Unless you are the owner of the acorn, or an invited guest, you must pass a perception test of 25 to even see the stump. However it is so ordinary, that even if you see it, there is nothing to show it as anything other then a rotten old stump. Only the owner and his guests can enter the abode, however it does physically exist, and so can be damaged. The stump has 100 hit points, and is immune to all non-magic damage. Should the hit points be exceeded, the residents of the stump will be forcibly removed, and take 6d10 force damage each.
Game masters, it is suggested that anything left in the stump for a month or more is considered by the stump to be a part of it. This includes any objects stored in the stump while in transit, should you players decide to use it as a storage location. Should that happen the items, would no longer be able to be taken out of the stump without dissolving and returning back inside. Additionally should the characters decide to stay within the stump for a month, they as well would be considered by the stump to be a part of it. The only way to release an object once it becomes part of the stump is through divine intervention, a wish spell, or basically whatever makes the coolest story.