I'm surprised how little skepticism there is about posts like these. A month earlier the user posted a comment about a mortar round in the same group, and posted a video about a security prank. Not saying it's fake, but it's far from obviously true.
https://www.lupa.cz/aktuality/na-redditu-se-resi-udajna-bomb...
On one thread on Reddit, an interesting thing is being discussed today. The user, with the nickname WhySoSadCZ, posted a photo of where an old bomb lies between the server racks on the ground. It is supposed to be a location in the Czech Republic, specifically in a server room in offices of unnamed smaller companies.
"No one has been in the server since the last person left IT two months ago and apparently took his keys," WhySoSadCZ writes that he was going to repair the air conditioning in the room and had to get in without the keys.
The user further writes that the business owner has no idea how the bomb took place there. He also states that the building has been evacuated and that the police have been involved here.
Police Spokesperson of the Czech Presidency of the Czech Republic, Jozef Bocan, however, told Lupu that the police did not carry out such an action. "We do not know anything about this description at this moment," he said.
I believe this is probably a deacitvated missle someone had as a curio (I see similar stuff used as door stops in military surplus stores). OP then decided it would be funny to stick it in a bundle of wires and tell people he found it.