There’s Something in the Sea was an ARG created to promote the release of Bioshock 2. It also happens to be some of the best Bioshock content released and I highly recommend it for fans of the series.
The ‘game’ involves playing as the character of ‘Mark Meltzer’ a journalist who starts investigating the disappearances of little girls. It starts out with a map of the world, with the locations of kidnappings, alongside their dates, marked on it. Additionally, clippings from news articles, notes, and the occasional picture, start getting added to it.
TSitS is strangely captivating, and I found myself practically glued to the archive site…so much, I ended up forgetting to do stuff in life, like eat. The story is relatively simple, but the characters are so well written that they feel like real people, aided quite a bit by the acting. I did, however, at times end up mentally screaming at Mark, but this was not because he was doing anything stupid, but because he wasn’t doing what I would have done in a particular situation.
There is a summary video of it on YouTube, but I’d recommend going through the original, as the video leaves out a lot of details and isn’t nearly as captivating.

• An Archive of TSiTS by Rapture Archives
  • Note: It requires Flash to run and Ruffle only properly supports phase 1. However, if you install/use a browser that supports NPAPI plugins¹⁾ and you install Clean Flash Player; you won’t have issues.
• There's Something in the Sea summary video by Inside a Mind