Sculptures may very well be the pinnacle of the art
world. In my opinion, the difference between a sculpture
and wall art is like watching the sunset or looking at a
picture of a sunset.
A sculpture is fully in your space.  You can
approach it, walk around it and interact with it.  The
dimensions of a sculpture provide a connection you will find
with no other fine art. However, as a general rule sculptures
tend to be more expensive than wall art.
There are several "types" of sculptures and you are
probably already familiar with most of them. First you have,
Marble, Stone and Wood Sculpture. This is perhaps the
most grueling of all media, because only through intense
labor can the sculpture be carved out of a single piece of
stone or marble or wood.
Marble, stone and wood sculptures fall under what is
categorized as take away sculpting.  With take-away
sculpting, the artist must mentally reach into the block of
stone or wood and see the sculpture within long before any
physical work begins. "After the artist has seen the figure
inside it's simply a matter of removing the unnecessary
stone." Well at least that's the way Michelangelo put it.
For those of us who are not Michelangelo, it's easy to
imagine how complicated take-away sculpting must truly be.
You have no second chances or room for mistakes.
The process is a one-shot deal, and sometimes far along
the sculpting route you'll discover a horrible flaw
imbedded within the stone; which was not apparent on
the surface 6 weeks or 6 months ago when you began
working on it.