Recs.
Updated
Minecraft is an indie sandbox building game with a voxel-based world. It has a survival and a free play build mode. The game can be played offline and with others over the internet.
Specs
Pros
Pro Great creativity tool
If you prefer building creative mode is the way to go. It immediately gives you unlimited blocks, the ability to fly, and immortality. This allows you to easily build anything you want without worrying about height or enemies. Things like giant castles, villages, roller coasters, and even unique builds such as the Enterprise from Star Trek. You can really let your creativity loose.
Pro Randomly generated worlds and distinct locations keep the gameplay fresh
Each new world is randomly generated, making for a different experience every time. There can be plains, rivers, beaches, ravines, giant mountains, hidden villages, and a lot more.
There are also 38 biomes, which includes snow, desert, forest, swamp and other biomes. Each one has its own set of unique blocks, plant life, and creatures.
You won't get tired of exploring above ground or underground because every location will seem new and exciting.