Hi Fernofai, thank you for checking my game! Regarding the controls, there is an Instructions.pdf file with the game archive that covers game controls, and the README.txt file points to the instructions, too.
Also, good point about the full bag, I definitely should add info about that (tip for the other readers: just go to the hatch, enter it, and go back to loot the rest of the valuables).
You can hide only if Vikings are not in your FOV, or if they are unaware of your presence. Color of the player character has three possible shades: white (standing in plain sight), gray (standing on the tile that could be used for hiding, but someone saw you hiding there), dark gray (player is actually hidden). It could be more transparent...
Notes taken, I'll try to improve the mechanics transparency in the next release. Until then, I'll add info to the game page.
I'm glad the game was fun enough that you decided to figure it out by yourself :)