Open your own world and character files and see your world as it is: the exact locations, the ground you have explored under the game's own fog, your map pins, your death and home points, and the bases, portals and graves in it. The files are read in your browser and never uploaded.
A world is a pair of files, name.fwl and name.db; a character is a .fch file. The easiest way is to drop the whole world folder on the page. With the object files of a new world (.chunks and the .chunk files) the viewer also shows bases, portals and graves. Without a data file, only new-style worlds can be shown, because their locations are generated from the seed.
Are my files uploaded?
No. They are read by your browser and stay on your computer. Nothing is sent anywhere.
Where are my files?
On Windows: the folder AppData/LocalLow/IronGate/Valheim in your user folder, then worlds_local and characters_local. With Steam Cloud the same files are under worlds and characters, and in the Steam folder userdata, then 892970, then remote. On Linux: ~/.config/unity3d/IronGate/Valheim. On a dedicated server: the folder you started it with, under worlds_local.
What are the dimmed locations?
Locations that exist in your world but that you have not visited yet. The ones you have found are shown in full.
Does it work for a world from an older version of the game?
The terrain is generated from your world's seed and generation version, so older worlds are drawn as they were made. Locations come from your world data file.