Luigi Mangione is locked up in a notorious NYC federal detention center known for its horrible conditions — and TMZ has been given the lowdown on his life behind bars.

Sources with direct knowledge tell us … Mangione is tucked away in “administrative segregation” at MDC Brooklyn — with a group of inmates separated from the general population because they require heightened security.

In the case of Mangione, he became infamous after being arrested for the high-profile murder of UnitedHealthcare CEO Brian Thompson — so he could be a target for other inmates. Hence, the extra security.

Our sources say Mangione’s locked up in a single cell — nobody’s rooming with him. But, the cells are close together and inmates frequently talk to one another.

We’re told there aren’t TVs in the segregation unit … so, there isn’t a lot to do during the day.

Luigi does get a chance to stretch his legs … enjoying one hour a day out of his cell in the rec pen — a large cage where he will be uncuffed. Our sources say sometimes there’s a basketball or a stationary bike in it, depending on which cage is used.

For his entertainment, we’re told Luigi can buy an MP3 player and songs through the commissary — if someone puts money in his account, that is.

Inmates are limited to $350 of spending a month — though for the holidays they’re given an extra $100 added to their limit.

As you know … Luigi is charged with fatally shooting Thompson in Midtown Manhattan earlier this month — with authorities throwing Mangione in MDC Brooklyn after he was extradited back to NYC from Pennsylvania.

Luigi Mangione Photos Launch Gallery

Luigi’s facing murder charges at both the state and federal level … and, he’s allowed to meet with his attorneys while locked up in MDC Brooklyn.

Diddy‘s locked up in the same jail … and, conditions there aren’t great. But, sounds like Luigi’s got a pretty simple routine as he waits for the trial.