Tannen Manor in 1971B.
Tannen Manor was a home located in Hill Valley, California in the alternate timeline where an elderly Biff Tannen traveled from 2015 to 1955 with a Grays Sports Almanac to make himself rich.
Biff had the plans for the manor drafted in 1971, but the zoning commission deemed that it was too large. Biff barged into the city council meeting, and demanded a vote to get his plans approved. However, Stanford S. Strickland objected, and the vote had to be unanimous. Biff tried to bribe Strickland by telling him that he would build a new gym for Hill Valley High School and call it the "Gertrude Tannen Memorial Gym". However Strickland told him that he could not be bought, which led Biff to go to more drastic measures.
He sent a box of cigars to Strickland at his office at the high school, with a note that made it seem they were a gift from someone who was happy that he stood up to Tannen. When Strickland lit one, it turned out to be a novelty exploding cigar, which exploded and set light to a pile of papers on his desk. When Mr. Strickland tried to put the fire out with the fire extinguisher, the fire grew out of control as Biff's gang had replaced the extinguisher fluid with an accelerant.
Biff sent a photograph of Strickland lighting the cigar in his office, which led to an investigation. Strickland was forced to step down as principal and as a member of the city council while the investigation was in process. With Strickland out of the way, Biff's mansion plans were approved.
The mansion was complete by 1972, when Biff held a ceremony for "Mother of the Year" there, declaring Lorraine Baines McFly the recipient of the award. However, the ceremony was just a ruse by Biff to get Lorraine to come to his mansion. She was disgusted, but her parents, Sam and Stella were overwhelmed by his wealth. Sam wondered if Lorraine would have married Biff if he hit him with his car instead of "that other kid".
Later that year, Biff's second wife, Jayne Mansfield, discovered a fallout shelter beneath the mansion. It was a shrine to Lorraine, full of portraits and sculptures of her, which disgusted Jayne and caused her to leave the mansion and divorce Biff.
In 1973, Biff shot George McFly in an alley and had a member of the Hill Valley Police Department, which he controlled, cover it up by pinning George's murder on Red the Bum, by planting George's wallet on him. With George gone, Biff was able to convince Lorraine to marry him, in order to help her family, who were all in financial trouble because of Biff's dealings through BiffCo.
After the marriage, Lorraine moved into the mansion with her children, Marty, Dave, and Linda. Dave was disgusted with his new stepfather, and in 1983 he joined the Hill Valley Civic Committee to try to stop BiffCo. He knew that Biff kept a safe in the mansion, so Terry planned to break into it while Biff and his family were at dinner. However, Biff stayed behind and caught Terry in the act. He had the police officers that he controlled beat him to death, and then had them run Dave out of town. With Dave gone, Lorraine feared for the safety of her other children. She sent Marty and Linda to boarding schools, with Marty's school being across the world in Switzerland.
After the construction of Biff Tannen's Pleasure Paradise Casino & Hotel, Biff and Lorraine moved there to live in the penthouse suite, and Biff moved his safe there as well.