level of organisation of proteins
Interesting protein structure trivia question!

Disulfide bonds form more or less spontaneously when two sulfhydryl groups from cysteines are close enough to each other in the proper orientation in a reducing environment.  So given this, its possible for them to exist, even though in most cases the distance between the cysteines in a disufide bridge is small and intra-domain. 

Inter-domain disulfide bonds are rare.  The most common example is that some immunoglobulin domains in antibodies have an intrachain disulfide bridge.  I also found reference to one in a starch synthetase from rice.  

In tertiary structure, the overall shape is an important one.  Globular shapes are the most common, but elongated protein folds, triangular folds,  rings, disk-like structures made out of wedges are popular examples of how protein structures can do amazing things when selection requires them to.