There are two ways to get in:
1. Through Tartarus wearing the Herald's cassock and then taking the elevator with the map from Army Headquarters.
2. Through the main entrance wearing counterfeit armor from Karl of the Dogs and Douglas of Rainbow's dog tag. He also needs to bring the items he was supposed to find—the list can be found in his personal journal after holding it.
So, you need to bring the following: an ultra-repair kit from Screamer's basement at the Dogs of Dusk, an encyclopedia from Mark of the NMP, the narcotic drug "Admiration" from the Healer of Rainbow, and a prototype plasma rifle from Christopher of Laivos.
You need to change into the counterfeit armor before reaching the location, otherwise patrols will notice and open fire.
First, on the approach to Olympus, you'll have to present Douglas's badge and the items you found. Then, talk to Captain Richards (don't call him "sir"), receive Scout armor, an obedience injection, and a quest to retrieve the chimera queen. We also learn that Jock needs some help.
We go to Jock; he wants Kelly, who works on the Organics floor; her boyfriend died in Tartarus (he was the recruit whose diary was found in the cave during the escape). We agree and receive an access card to Organics 031. It's best to complete this branch first.
Kelly is in the room across from the elevator, standing next to Gray. You can also talk her into it this way, developing the theme of stupid, drunk, and hairy guards who can be matched with her. After completing Technician Moreau's assignments, we learn from him about Kelly's sloppy work habits, and we can use blackmail. In any case, if you send her to Jock, he'll abuse her, but the main character will receive a Colt Python (arguably the best melee weapon, although you could have already found several by now) and a hefty karma penalty.
Alternatively, you can first go to the top floor (stairs in the upper right corner) and pick up a Stamina Potato (near one of the workbenches, out of sight behind the wall; Shift will do the trick). You should also talk to the technician, Moreau, standing just below. He needs a slave from Tartarus to tune the workbench (perhaps the workbench can be repaired yourself with a high repair level, I'm not sure). You'll need the Herald's Cassock, otherwise the guards will aggro (though you can also complete the mission in combat mode), and an access card from Army Headquarters (or take the detour, through the main exit and the Metro station to Tartarus and back).
We bring the slave from Tartarus to Moreau, receive a reward, sleep for a couple of hours, and receive another task: retrieve energy cell 051 from the engineering floor. We take the keycard, immediately speak with Zachkiss on the floor, then go to the far upper corner to see Dick, who wants a clone of his wife, Beatrice. We go to Gray, then to Moreau, and then to the biolab.
In the biolab, we take out the undead and collect the bioessence from one of the lockers in the basement. Return to Moreau and give him the flask. We take the Beatrice clone to Dick, where we receive the electronic code to the safe—2249—where Zachkiss's access card is located, which we'll need later.
Now we can go to the Chimera Lair. First, we need to quickly inject the Chimera Queen with a docility injection; she'll deal with the rest almost single-handedly. Don't forget to collect the Chimera Fangs for the Screamer from the Dusk Dogs. In the generator room downstairs, grab the Potato of Power and the Lilith Rifle, which breaks the arm's arrow, from the locker. We head back to Olympus, stopping by Screamer's place in the Dusk Dogs along the way—give him the Chimera Fangs and kill him.
We reach Gray; he wants to set the Chimera on Zachkiss. We go to floor 051 and take out everyone with the Chimera. The power goes out—go to the balcony (there's a passage on the left), down to the right and find a door, then up to the left and some terminals there that will turn on the lights (there's no logic to this).
Return to Gray, who gives you the password to the power panel—2358—and tells you how to unlock Zachkiss's access card—computer D-3. Use the Physix card on the panel in the office, then on computer D-3 (the grid around the edges of the map).
Floor Physix 063 is just below the Taylor elevator; he needs the Lumenier armor servo. Let's go look for a patrol of servants of light; they can be found in the mountains in the northern part of the map. Remove the servo from the patrol leader's corpse and return to Olympus. As a reward, Taylor will give you the AS-2000 MK-2 armor for testing, which you must wear for two weeks. There is no further development.
In the upper right corner, Professor Crank—if you speak to him without Baraka (there's no option to go and find her)—will ask you to bring him scientist Schwein from Laivos. You don't have to use the obedience serum; you can simply persuade Schwein to go to Olympus for a consultation. Next, we witness the torture of a poor scientist. And a dead end (I couldn't find any further progress).
We arrive with Baraka, receive a quest to find her, and immediately turn it in. We receive a keycard X2 and head to floor 096. Captain N34 is there, but instead of testing Baraka, we'll have to test the defenders' armor (which costs about 60 health points). Then there's the same pointless running back and forth to Krank, and an equally unimpressive expedition to destroy a tribe of cannibals in the Oasis.
Now it's completely unclear why - we go to change the access code on the server on floor 079 - there are terminals in the middle of an empty hall. We enter the code 1234 (or rather, we accept the proposed option), and then, just for fun, we head to control floor 103. There's only one option - through the gate, and then there are many options... In terms of the order of destroying the turrets. The protective screen is also a mindless shooting spree.
Overall, the ending was disappointing, both in terms of quests and combat.
Source: nuclear-city.com.