Cave Flight

Cave Flight is a side-scrolling shoot'em up game for the ZX81 microcomputer that was released in 1985. It was designed by René Straub as a "listing game", meaning that the game was not released on a physical disk that could be bought in stores, but that the game's code was published in a magazine. Cave Flight was published in the June/July 1985 issue of the German magazine "Homecomputer". It consists of about 1.5 pages of Sinclair Basic code and was René Staub's first published game. He developed it in one to two weeks, sitting in the living room in front of the TV. 

The concept of Cave Flight is as simple as it is relentless. The player controls a flying object, represented only by characters, through an ever-changing cave system. The object of the game is to collect as many diamonds as possible and beat the high score. The challenge lies in avoiding the spikes of the cave. The player has three lives and loses one if he crashes into an obstacle; if all three lives are lost, the game is over.

Source: https://stage.chludens.ch/games/cave-flight/