Big Lock is an enourmous dome prison with only a single gate in the front for only supplies. There are several lasers and land mines around the structure for intruders frozen tundra for 50km radius
On the inside there appears to be very few prisoners aside from Diego and Alexander, although some other Yami armed members are imprisoned there. The prison chanbers that hold Diego and Alexander are very confined. There are several security cameras in the prison and it's rather dark inside, and is under constant surveillance.
Big Lock is a prison created to hold the strongest Killing Fist user's of Yami.
Big Lock is considered the largest prison in the world and is the only place strong enough to hold Yami Elite master class fighters such as Diego and Alexander at bay (however, both fighters stated they could escape anytime they feel like it and only will do so when they feel something worth breaking out for will come for them). The prison itself is very large and near impossible to penetrate, having land mines in the front and lasers around the building,while The Prisoner 's cell have an electric gate instead of grating with enough power to burn anything pass it to crisp (while Diego seems able to withstand it and only his clothes got burned).