Nintendo has announced they are offically closing the Miiverse on November 7 2017. Nintendo says before it closes, users are able to download their content submitted to the Miiverse. Source
The Miiverse was the social network for the Wii U and the 3ds, starting in 2012. Users were able to create and share content within the platform iteself, and many games supported unique content in the game itself. Take Mario Maker for example, players are able to leave comments through levels. Features like this will no longer be available.