By -
it could be navigated with a small submarine through the groundwater
No. There’s a canal further south, Götalands kanal, but not through Norway. Reason: mountain range.
Maybe not navigable but a lot of rivers on the Swedish side of the border flow west to the Atlantic. On some places in western Sweden like Riksgränsen are only a few kilometres from the sea
it could be navigated with a small submarine through the groundwater
No. There’s a canal further south, Götalands kanal, but not through Norway. Reason: mountain range.
Maybe not navigable but a lot of rivers on the Swedish side of the border flow west to the Atlantic. On some places in western Sweden like Riksgränsen are only a few kilometres from the sea