The Beanstalk

From my Weird Stuff That Won't Get Played file:

Beanstalk - The climbing vine of any of a large variety of legumes.

Beanstalk - SF geek slang for a space elevator.

This one's both.  It's not exactly natural, but it is alive.  It isn't exactly an elevator as such - more of a bridge.  If you've got the time and inclination, you can walk all the way up the stalk to the counterweight.  This would generally take about three years to get to the main station at the halfway point (14,625 miles or so).  The thing about large foot bridges is that they are seldom unoccupied.  No, not trolls (mostly).  Medieval bridges were lined with shops and houses like any other street, just moderately cleaner (just as easy to chuck the refuse in the river as in the gutter) and often with mills in the stream.  The main stalk is hollow and has a horizontal cross section about 250' across, or about the same area as one of the original World Trade Center towers.  The assorted "floors" vary in height, but are usually less than 30 feet.  There are various types of passageway that allow access between levels - it's a living plant, but was designed by wizards (or someone sentient and a bit off, anyway).  There are also access points to the outside, where leaves the size of small baronies become archipelagos in the sky linked to the main stalk by their tendril.

The takeaways:

• Live, plant-based wizard's tower.  Height not measurable by conventional means.  A little under 30,000 miles if you must count.
• Surface area roughly that of Australia.
• There's stuff living there.  Some of it's a little strange.

Owlbear

No, that's a bare owl.

The first one was more disturbing.

Number Appearing:  One's enough

Size:  Too big

Armor: Fat, feathers, intense burning rage

Resilience:  Very.  Too angry to recognize lethal injuries.

Intelligence:  Not so much.

Communication:  Violence, mostly.

Disposition: Hangry.

Violence:  Very much so.  All the appendages end in sharp.

Enemies:  More or less everything, but especially wizards.

Aims:  Kill.  Eat.  Hopefully in that order.

Peculiarities:  Interact strangely with wizardry.

Treasure:  Not really.  Maybe a tacky rug if you're careful.

Wizards bend Reality in uncomfortable ways.  Owlbears are Reality telling them to stop.  The enormous eyes can see magic, even in complete darkness.  Especially in sorcerous darkness.  Magic is tasty.  Owlbears devour spells as they devour wizards.  If the wizard is particularly alert and starts casting before the chomping starts, they devour spells before they devour wizards.  The magic makes them stronger, angrier, and harder to kill.  Oddly, they'll get the same rush from devouring scrolls, wands, spellbooks, and potions (oftentimes plus the potion effect).  In the absence of sorcery, they are merely nearly silent nocturnal ambush predators that can out-sprint a horse.

Animate Structure

Some magic is about sacrifice.  A castle can have a garrison and sit in the middle of a friendly (or at least ethnically loyal) population and change hands regularly.  A wizard's tower can stand alone for centuries.  Because every now and again, some idiot gets an army together and tries to take one.  Their legends discourage future attempts.

This is more of an item ability than a spell.  A wizard with the correct property rights may once (not once a day, once a month or once a millenium, but exactly *once*) activate a magical structure to defend hearth and home.  This takes a bit of time (one full turn, ritual casting, or however your game covers "about as long as it takes to brew a cuppa without a fire going").  The wizard must have legal title to the place, either inherited, elected, or constructed.  The structure fights as an enormous golem, running along on its pillars, columns, or flying buttresses and steamrollering anyone that doesn't get out of the way.  It moves either the length of its footprint or its height, whichever is greater, in a straight line every round.  Everything that doesn't get out of the way is essentially getting hit by a rockslide.  The building is still a building - its ability to take damage is neither lessened or increased.  The structure will fight for one round for every year that the wizard has lived in it, plus a round for every five years that previous owners in the line of succession have not used the ability.  At the end of this time the structure must make a Saving Throw - success means it still stands, if it is able to on the location it ends the duration in.  Failure means it collapses in a pile of masonry, its wizard pilot usually escaping the collapse by one sorcerous stratagem or another.  The duration on this ability means that it is normally only used in defensive circumstances.   But there was this one resurrected Pharaoh...