The Witness Pre-Installed Game
Your only way to interact with the island, to open doors or create paths or otherwise make things happen, is to draw lines, thereby solving puzzles and occasionally operating switches. Your first act is to draw a line through a square on a door to open it, and once you’ve walked through into the island you’ll come across hundreds of more grids to be marked in much the same way. The rules change – sometimes you need to make sure that the line separates marks on the grid or forms particular shapes – but the process is the same: find a puzzle, solve it, witness the effect (an opened door, a new pathway, or just the activation of a new puzzle) and move onto the next.