One of the most influential games of the 1990s, and perhaps one of the greatest entries in the entire stealth genre, celebrates its 20th anniversary this month. Do you know which game this is?

Metal Gear Solid arrived on the original PlayStation on September 3, 1998. Though it wasn’t the first game in the overall Metal Gear franchise, it did introduce the character of Solid Snake to his widest audience yet. The game followed Snake’s exploits as he infiltrates a nuclear weapons factory in order to rescue hostages and eliminate the threat of terrorism. The story canonically takes place six years after the events of Metal Gear 2, with Snake being forced out of retirement in order to take on the new threat.

Solid Snake must also confront his twin brother, Liquid Snake, who is bent on using the massive mecha known as Metal Gear REX. Solid and Liquid are revealed to be the results of a project known as “Les Enfants Terribles” in which the legendary soldier known as Big Boss was cloned.

As a stealth game, Metal Gear Solid requires its players to navigate Snake through the facility without being detected by any enemies. Snake can be detected if he’s caught in an enemy’s field of vision, which can be tracked via the “soliton radar” function present on the screen. Snake can fight characters if he has to in order to escape from a situation, but it’s encouraged that the player avoid violence wherever possible. Snake can also make use of the now-infamous cardboard box as a disguise in order to hide in plain sight.

The game was originally planned for the 3DO in the mid-1990s, before development switched to the PlayStation in order to make use of its superior hardware. Metal Gear Solid was critically acclaimed upon release and is considered one of the most impactful and influential video games ever made.