Most criminals who are locked up as a punishment or to await trial are just confined in regular cellblocks or jails, but not all of them. Some are so dangerous that ordinary prisons just will not hold them. Others have secrets that cannot be allowed to be spread, or their crimes are so dreadful that they deserve a greater punishment then normal incarceration or even execution. In yet other cases the ruler had a nasty sense of humour...
Incarceration in the Cosmic Era, adjustable for futuristic and dystopian settings
One of the largest and most famous cryodetention centers operated by Creative Incarcerations Corp
"Ye thought the orbital penitentiary around Venus was hard ta endure? That place is a vacation spot compared to Davy's Lockdown! If the guard borgs can't find an excuse ta peel the skin off yer bones and the inmates don't use ya for their bettin pool, the pressures o' bein that far beneath the waves will drive ya to the brink, mark my words!"
An underwater prison with a dark past, suitable for any sci-fi, neo-dystopian, or cyber punk setting.
Sessiliths (name based on the word sessile) are gargoyle-type creatures which are stationary, attached to the stone of whichever foundation they are bound to. Though they can move their extremities and limbs they are unable to move away from their particular perch. In lieu of swooping down and attacking like their mobile cousins the gargoyles proper, sessiliths are equipped with their own brand of mischief. The creatures are all able to verbalize and thus usually hurl vile insults and curses upon passersby. The cumulative effects of dozens of sessiliths cursing, screaming, and speaking in tongues, can have an effect of temporary confusion (or even discord) in those forced to listen to the shrieking stone gremlins.
Additionally, most possess the ability to "spout" or spit forth various undesirable projections, such as tar, boiling water, or even acid. While they can usually be avoided easily enough or even destroyed (their "bodies" feature the same defenses as gargoyles), sessiliths are usually placed in such a way as to hinder all trespassers and interlopers, narrow corridors, claustrophobic tunnels and other related "gauntlets", where they cannot be easily avoided. Like gargoyles, sessiliths come in all sorts of grotesque shapes and sizes, though they tend to resemble tiny horned devils, demonic amphibians, or simply distorted faces and heads, more often than not.