After you have mastered the basics of woodturning then your only limit is your own creativity. One of the most challanging projects, conceptually and technically is reversed turning, where you turn both the inside and the outside of spindle like objects. These can be just artistic objects, or beautiful candle holders if you cut off one end to open them up. You are right, the one in the photo is missing a piece of one leg -- it fell off a shelf and I decided it looked even more exotic like that so I never glued it back together. The real problem with reversed turning is understanding what a form in the first stage is going to end up looking like in the last stage.
You start by gluing together 4 square sticks of wood, but you put butcher paper or brown mailing paper inbetween the sticks.
That will hold them tightly together, but allow you to split them apart once the first shape is turned. You have to leave some square surfaces during the first turning, or you won't be able to reverse them.
Once split apart, reverse them so that the cut shapes are on the inside and glue the squares together, without any paper. This is now a permenant joint.
Now you simply turn the other side, stopping often to see if you are going to break through.
You always wear a full face mask when doing turning like this because I guarantee you will explode some apart. I would suggest starting with a wood like Mahogany because it is strong, easy to cut but has a very even grain. There will be enough surprises until you understand the reversed shapes, so don't try to deal with crazy grain with your first reversed turnings.