浦原は二番隊のとき看守だったらしい
Urahara was a prison guard while at 2nd division.

also:

蛆虫の巣は十三隊の危険分子を閉じ込めておくところ

浦原「見てください　あそこにいるのがここでただ一人檻の中に入れられてる危険分子ッス」

「浦原喜助か…何のようかネ？こんな処に」

浦原「あなたにようがあって来たんスよ　涅　マユリさん
　僕と一緒に　ここを出ちゃくれませんかね？」

The Maggots nest is where the Gotei 13 keeps all dangerous specimens.

Urahara: That place is a single jail specifically for dangerous specimens.

"Urahara Kisuke what are you doing in a place like this?"

Urahara: I came here cos I have business with you Kurotsuchi Mayuri san, could you please come with me?

砕蜂は出てたよ
Soi Fon appears xD

mona added:

罪人っていうか、規定で危険っぽいって判断された人を集めて閉じ込めてる
中にいる人たちは何も悪いことやってないけど閉じ込められてる
マユリ様だけは檻に入れられてるから何かあるのかもしれないけど…

The people there are not "criminals" as such but rather people who seem dangerous to Soul Society in some way. They are locked up even though they haven't really done anything yet and Mayuri is in that cell all by himself.

mona added:

罪人っていうか、規定で危険っぽいって判断された人を集めて閉じ込めてる
中にいる人たちは何も悪いことやってないけど閉じ込められてる
マユリ様だけは檻に入れられてるから何かあるのかもしれないけど…

The people there are not "criminals" as such but rather people who seem dangerous to Soul Society in some way. They are locked up even though they haven't really done anything yet and Mayuri is in that cell all by himself.

Mankind a écrit:pacecat @ BleachAsylum a écrit:

mona added:

罪人っていうか、規定で危険っぽいって判断された人を集めて閉じ込めてる
中にいる人たちは何も悪いことやってないけど閉じ込められてる
マユリ様だけは檻に入れられてるから何かあるのかもしれないけど…

The people there are not "criminals" as such but rather people who seem dangerous to Soul Society in some way. They are locked up even though they haven't really done anything yet and Mayuri is in that cell all by himself.

Mayuri s'est fait enfermer volontairement parce qu'il s'estime dangereux pour la Soul Society ???

Bleach -106 ~originally posted by Drake at Pantip

At the 2nd division, it was reported to Yoruichi that Urahara had headed to "the Maggots Nest". Soi fon was going to oppose it but Yoruichi told her not to worry and that Urahara must know what he is doing if he is taking his vice captain to that place.

Urahara eventually manages to drag Hiyori along with him. While walking there he tells her the history of the secret mobile corps. It was established separately from the Gotei 13 and the Shihouin family has a lot to do with it. Therefore the leader of the Shihouin family is given the rank of captain in one of the Gotei 13 divisions, that division will have a very close relationship with the secret mobile corps.

The current leader of the family is Yoruichi who is the captain of the 2nd division. The members of the division also have to take up a position in one of the 5 sub-divisions of the secret mobile corps. Urahara was included in this, the sub-division he once took responsibility for is the 3rd sub-division of the secret mobile corps which is called "Kanritai" which means “the Penitentiary Department.”

One of this department's duties is to confine shinigami who have a high possibility of bringing danger to others, which makes them also considered an obstacle for the gotei 13.

Urahara further explains that it's to imprison "the cause of danger". He points towards the northern part of the 2nd division which has the large prison where these prisoners are kept. It is known as the underground for special imprisonment or, the Maggots nest.

It is a rule that they have to leave their Zanpakutou with the guards at the gate. The area inside the prison is like a large room. There are tables and chairs for the prisoners to relax on as the prisoners are allowed to live freely inside this area. Urahara warns Hiyori to be careful while walking through there because even a prisoner might look calm, there have been times when a prisoner went crazy.

Hiyori asks what crimes were committed by them but Urahara replies that they have done nothing. They are simply judged as "dangerous persons" by the law of Seireitei. So they are imprisoned to avoid a situation where they can bring harm to others. He then asks her if she can recall whether anyone has resigned from the Gotei 13, Hiroyi answers that there are 2-3 persons.

"The Gotei 13 has no 'resignation' system but only suspension and elimination of the name if they are absent for too long. There is no resigning as it means being put in the 'special confines' for the Gotei 13" says Urahara.

In conclusion there is no such thing as resignment in the Gotei 13, which is a noble organization, once a person is accepted into a division. These dangerous people who can not go along with the organization are imprisoned and it is made to seem like they have retired to everyone else.

Urahara has always had doubts that these prisoners should be locked up as he thinks their powers could be used for something great. While they are talking a giant prisoner goes crazy and charges at Hiyori. Urahara takes him out with his bare hands. He tells Hiyori, who is shocked, that the most important requirement when being appointed head of this department is that the candidate must be able to defeat every prisoner in there with his/her bare hands.

Then Urahara takes Hiyori to the end of the pathway. There is a medium sized jail that is heavily locked. "Look at that, Hiyori-san", he says. "Over there is a dangerous person whom we have to keep separate from the others.”

The person who wears a white kimono sits there in the darkness."Urahara Kitsuke?" they ask.
"What brings you here?"

"I have some business with you", replies Urahara while walking towards the cage. He looks at the prisoner while smiling. "Kurotsuchi Mayuri-san."

There is no response from Mayuri but the former jailer continues, "please come with me."