Speaking of Greg Bear; one of my all-time favourite SF books is his novel Eon. It was my gateway drug into English-language grown-up SF; it came out in 1985, I was 13 and had pretty much exhausted what was readily available of nerd-genre literature in my native Norwegian, thus was forced to get my English-reading skills up to scratch. Picked this up randomly in a bookstore because the cover looked promising (as one did in those days).
Elevator pitch: It's about 20 years in the future from when the book was written. The world has narrowly avoided a full-scale nuclear war already (the book doesn't go into much detail on this, but apparently the US and the Soviets both fired an ICBM or a few at each other, lost a city or three, and were able to stop and de-escalate back into Cold War normality) but the threat is very overhanging and real. Boom, a large asteroid appears out of deep space. But it doesn't hit the Earth, it decelerates and enters orbit. This is clearly not natural. It's quickly discovered that it's a hollowed-out colony / STL starship, and explorers are sent. But it's abandoned / mothballed. But it's not alien, it's human. From the future. And it's really weird because it's bigger on the inside than the outside, as it connects to an extradimensional tunnel that may be infinite in length.And then things get even weirder.