You will find this location somewhere in eroded badlands. The image shows the back of the building.

On the back, you will see a ladder and a door. The front has an open entrance, so you can get there from either side.

Going up the ladder takes you to a Team Rocket Scout on the roof.

Behind the scout, there is a ladder which takes you to an antenna.

Inside the hopper at the antenna there is a Darkinium-Z.

On the first floor, there is a Team Rocket Grunt and a chest with slate balls and black apricorns.

On the second floor, there is a Team Rocket Agent with a data monitor and a barrel. Take the data monitor - you will need one for Mewtwo. The barrel on the left has some relic coins.

There are some bookshelves in the corner that have enchanted books in them.

On the third floor, there is a Team Rocket Scientist. Behind him is a fossil analyzer - if you don't already have one, take it. The barrels have paper and books.

The other side of the floor has a barrel and the Team Rocket Spy. You can see him in the background.

Go up the stairs close to the scientist. On this 4th floor, you will find 2 barrels - one has a dark gem and both will have paper and books. At the other end of the floor is the Team Rocket Officer, with a PC behind him.

Go back down to the 3rd floor, go up the stairs that are next to the Team Rocket Spy. You will come up to the 4th floor again but this time on the other side of the glass from the officer.

Going up another floor and some ladders, you will find Team Rocket General Archer.

Defeat General Archer to proceed. He has a strong team with Houndoom, Muk, Magmortar, Weezing, Probopass, and Golbat.

After beating him, make sure to loot the two barrels in the back. They have ominous keys. Keep hold of at least one trial key - you will need it for the Radio Tower location.

Break the floor beneath you in the room with Archer and you will drop into a room with Admin Atena.

Winning against Atena nets you the Cloning Catalyst. You will need this for Mewtwo.