The Dangai Precipice World was one of the integral plot lines to the first Bleach feature length film Bleach: Memories of Nobody. It somehow spawned birth to the Valley of Screams which was revealed to play a role in the creation of Blanks.
Naturally, because the pathway exists to protect against Hollows and other spiritual entities entering either world, it had certain defenses put up. Hence why Shinigami are only ones who can truely use the path efficiently both from and to the world of the living.
The Kouryū is a current that constantly flows through the Dangai to help prevent the invasion of any hostile creatures. The current can stop them completely, and even getting one foot caught by the current will mean the entity is stuck there forever. It encompasses the walls of the Dangai and capture anyone that makes even the slightest level of contact with them. Whilst moving through the Dangai Uryū Ishida, with Ichigo Kurosaki whilst he was trying to save Uryū and Zangetsu, almost got caught in the current. Luckily however, only his cape was caught and Chad was able to break him free. Upon their escape from Soul Society, Orihime Inoue was able to use her Santen Kesshun to block a Janitor, comprised of Kouryū, and escape unharmed. However, Yoruichi Shihōin berated her for this as only the shield part of the ability was touched, if any of her Shun Shun Rikka had been touched by the Kouryū she could have killed them all. Also, if a persons Zanpakutō is used or revealed, they will also be captured by the current.
 JanitorsShūsuke Amagai, he uses his swords projectile capabilities (ths protecting himself from the current) to obliterate it. This shows with sufficient power, a Janitor can be 'killed', at least from a distance. During Deicide 9, Aizen was shown to destroy the Janitor with his bare hands without getting caught, how this was done is currently unknown.
 Time-Space Difference
Being a different dimention seperate of that of the Human World and Soul Society, it holds a totally different time zone from each of them. For example, Ichigo's training lasted 10 days in the living world, waited 7 days for the Senkaimon, and spent 5 days total afterwards before his 3-Day Bankai training. Which logically would means he spent a total of 25 training, which at the time would have led to it being a day before the execution of Rukia. However, as luck would have it after being chased by the Janitor, Yoruichi and the Ryoka entered a twisted time-space tunnel when they escaped the Dangai, making their actual arrival to Soul Society about 7 days earlier.