Back in the 80's Usborne published a variety of coding-related books. They'd usually contain listings for creating different software programs. My favourites were the ones that concentrated on building games, and one of the first ones I ever copied (by myself) was a game called "Trip into the Future". It seemed like a good starting point for my #1GAM 2016 journey.
You're in a spaceship and want to return at a specific point in the future. The tricky part is balancing the internal and external times. The game is based around the theory of relativity, so time flows differently depending on how close to the speed of light you travel.
It's not a particularly complex game, but the memory of it has stuck with me over the years. This version is web-based and has some really (really) bad ASCII art.
If you're interested in seeing the original source code for this and a whole bunch of other games, you can download the book from the Usborne website: Computer Space Games