Video games were hugely expensive when I was a kid, even though they were massively simple affairs, but you only needed less than five bucks to get into a whole world of adventure in the brilliant Fighting Fantasy books. Especially when they went open world.
They were a natural progression from the Choose Your Own Adventures books, offering up a tonne of sword and sorcery and adding more dice-based gaming to the storytelling as you picked your way through the narrative. They were still nowhere near as complex as the full role-playing adventures in Dungeons and Dragons, but they were the next step.
The first I ever got was Forest of Doom one one mid-80s Christmas - I'd seen them in the shops and had been begging for one - and I hid in my room to play the shit out of that game all that afternoon while all the other kids were outside in the sun. I still played it properly with the dice and everything, although after a few books I just straight-up cheated and went through the book assuming I win all the fights, because it was such a bummer to just stop a story dead because you rolled three ones in a row.
As the first in the series, Warlock of Firetop Mountain set the template, with barbarians and monsters and evil magicians and tunnels and death traps everywhere. But authors Ian Livingstone and Steve Jackson were willing to bend that template as soon as possible, and got out into the dungeons and into the stars, like the fourth book Starship Traveller. (Although this was one of the few that I never successfully completed, because there was always a point where you got stuck if you hadn't picked up some sort of key information from some side-trip, and that was that, and I still feel a bit bitter about it).
Scorpion Swamp was particularly memorable, because it required you to draw a map, and gave the story more of an open world feel, where you could go anywhere It would be more than another decade before Grand Theft Auto's creators even starting thinking about an open world game, but it was already there in these cheap books.
They fell heavily out of fashion within a couple of years, but I've still held onto many of the. Especially those early ones, which had terrific covers, if nothing else. Maybe I'll give them another go. I probably won't bother with the dice, though.