The "Windows to the Worlds" marketing campaign for the space RPG has inspired players to hunt down all 1,001 unique advertising billboards and share them on the game's official Discord server.

The details:

Bethesda has confirmed that the billboards, which are numbered 1 to 1,001, are now being placed around the world. The billboards feature unique images of the game's planets, ships, cities, and more. The company's official Twitter account is also encouraging players to share their discoveries in the company's Discord server, with the ultimate goal of finding all of them.
So far, we know that some can be found in London (via VGC), with a few bearing the numbers 118, 210, 376, and 402 being spotted and photographed at various London Underground platforms. A fan also noticed what appeared to be one of the advertisements at first glance on an Australian tram, though it did not have an identifying number.
It's unclear how widespread the billboards are or how long the campaign will last. Fans are also wondering if Bethesda has any plans for a reward if players find every single one in the coming months, or if it is just a cool marketing strategy.

More gaming news:

The lead designer for Starfield, Emil Pagliarulo, revealed that Bethesda considered giving the player character a voice, similar to Fallout 4. According to the designer, the studio hired a voice actor to record a few lines of dialogue, which led to the idea being scrapped in favor of a silent protagonist.
Microsoft has quietly ended its popular Game Pass deal, which allowed players to secure a two-week subscription to the service for just $1, just days before Starfield's early access launch. The original deal, which allowed players to receive a month's subscription for a low price, was discontinued in March and replaced with a revised version in July.

Bethesda has scattered 1,001 unique Starfield billboards across the globe