A Dyson sphere around a black hole
The whole concept of a Dyson sphere is kinda idiotic.  Any civilization that is capable to build one, it is probably able to work out fusion energy very efficiently.There is no point to go and harness energy around a star or a black hole, when you can just produce it locally with a lot less resources/waste and materials.  The sun itself is actually very inefficient in producing energy.There is no need to harness the sun million of km away,  when you can recreate it in your home planet. The only way to produce a dyson like of sphere, is to tame an over-heated sun, and reflect away un-needed energy.  But there is no point to build one to just harness it.It makes great sci-fi stories, but that's about it. Scientifically, it just doesn't make sense.