Short answers, pulled from the story.
The Soviet Union launched Salyut 3 on the 25th of June 1974 as a secret military outpost disguised as a civilian facility. Vladimir Chelomey designed these stations to conduct reconnaissance missions without Western suspicion while appearing as peaceful orbital laboratories.
Salyut 3 contained three distinct sections including an airlock chamber, work compartment, and living compartment with water recycling facilities known as Priboy. The station featured exercise routines using a treadmill and Pingvin suit, sleeping arrangements with standing stations and foldaway beds, and entertainment options like a magnetic chess set.
The Agat-1 Earth-observation telescope dominated the work compartment with an optical resolution better than three metres according to post-Soviet sources. Cosmonauts used wide-film cameras to observe targets at Baikonur and developed film onboard that could be scanned by a TV imaging system within thirty minutes before broadcasting images back to Earth.
Commander Pavel Popovich and flight engineer Yury Artyukhin spent fifteen days aboard Salyut 3 after Soyuz 14 docked on the 4th of July 1974. They launched from Baikonur Cosmodrome on the 3rd of July 1974 and undocked safely to return to Earth on the 19th of July 1974.
Soyuz 15 failed to dock because the Igla rendezvous system malfunctioned preventing manual docking procedures when Commander Gennadi Sarafanov and flight engineer Lev Demin approached the station. The spacecraft came within forty metres of the station before limited battery life forced them to de-orbit and land after only two days.