An elderly woman whose taste in clothing is questionable carries a large black and lavender carpet bag that is at least two feet long and deep with a minimum six inch width. Her wardrobe is otherwise comprised of well-worn army boots, flowery pantaloons and skirts, velvet vests and jackets, (sometimes several,) and very expensive-looking black silk gloves when needed, under knitted mittens. Her hats are usually floppy-brimmed straw hats, but she sometimes wears a brown leather hood with a chinstrap. Regardless of her headgear, she will affect a billowy gauze scarf that appears once to have been white.
She is, to adults, a no-nonsense elder who expects everyone to do as she says.
She is, to children, that kindly Granny who always has a piece of candy for them.
Her purse is the doorway to a pocket dimension. It stretches open enough to allow a creature or object up to six square feet in cross section to pass through. The object must fit into a 16'x4'x16' space inside the opening.
A person entering headfirst will quickly realize gravity is toward the bottom of the purse. There is also a ladder. One can climb down about twenty five feet or so to the floor of what appears to be an excessively cluttered room.
The ladder is hinged and can be lifted out of the way. The room is, (or would be,) a sixteen foot square, except for the shelves, bureaus, trunks, and armoires that fill both sides of an aisle down the center, from doorway to fireplace. Two places appear carved out of the clutter, one of which is a bed, located on the left side near the fireplace, and the other is a tea table flanked by a pair of matching chairs and an ottoman on the right side by the window. (The other window is obstructed by a chifferobe and the bedframe.)
The fireplace is cluttered, and there might be risk to the contents of the room if anything hotter than a hibachi burned in it. However, all the supplies one would need to light and keep a small fire going are here, along with cooking utensils, basic spices, and dried foodstuffs.
The alley kept free of debris runs from the fireplace to the door. Looking up one sees into blackness. The only detail one can see is blackness, into which the ladder ascends.
The door opens to a mowed lawn leading down to a lake or wide river. Outside one can see a blue sky brighten in the morning, fade in the evening, and after a very long twilight darken to starry brilliance. Then the long twilight of dawn eventually gives way to brightening day.
A dozen trees of various ages cluster or scatter, giving dappled shade in the daytime to the sixteen by sixteen cottage at the top of a gentle slope in all directions to a circular moat that flows counter-clockwise at a lazy pace. One would have to swim this moat to get to the semi-forested slopes to the very near, (perhaps within 2 miles,) tree-line horizon. Swimming or wading the river is neither difficult, nor dangerous. The best that can be said of the far side is that interesting plants are planted here and there around it. An herbologist might be very interested in the variety and quality of many medicinal plants here, and an alchemist might identify more useful plants as well. There is a large quantity of none of these.
In a quiet grove on the edge of the pocket dimension is a fairy grotto. The twisted tunnels beneath ancient hollow trees lead to rows of dangling red and purple flowers, which the wee folk use to find their night's rest.
The only occupant of the grotto is Daelar the Fairy Sorceress.
She is Granny's familiar who spends a great deal of time in the shape of a brindled brown cat with white at the tips of its toes and tail. Daelar is curious, but does not mind the company, especially of children, with whom she plays.
Granny was an ancient silver dragon who wished to survive the war without revealing her true nature. She saved a village worth of children, and sometimes their parents, over course of the winter invasion. Of course, in your world she might be a hag of some sort collecting buffet for a night-in with the girls. Or something else.