The Vikings believed ghosts stood up from their graves and were physical beings who could attack them (even come in flocks to do so) or spread plague. They believed them to be evil, dangerous and vindictive. (which kinda begets the question of what they had to be vindictive of, but yeah...)
In our folklore we also have draug, which could be both land and sea based, but for the most part I've heard of them being sailors who died at sea and come ashore to drag people put to the sea with them. I've read some scary (fictive) stories about them.