If there are big, rare, deadly sea monsters in the deepest depths... there should be some kind of "warning" when the player is coming close to them. I mean, it's really dark in deep waters... and even if you had a light spell, it wouldn't lighten up much in front of you. The player would need some time to flee or prepare for a fight when he or she approaches a sea monster, I think :confused:
Perhaps a sea monster can make make a frightful sound at the exact time it notices the player... so that the player at least have a few seconds to either try to flee or bring up a weapon or spell. I think this would also make it even more exciting and scary
Or perhaps a sea monster can have this light on it (some sea creatures in deep depths in our world have some thing like this to lure other creatures to get closer...).
Player when seeing the light: "Oh there's some shiny light down there, deeper in the water... strange, perhaps some old magical item or ruin? Interesting, I should check it out."
When player gets closer: "HOLY MOTHER OF !#"&(¤%" -swims as fast as you can-
I was just thinking about this today at work. (Obviously very busy.) I was thinking the warning could go a little like something from a scene in Good Omens by Terry Pratchett and Neil Gaiman. Here's an excerpt. Not word for word, but fairly close. The bolded bits are the most important parts. I put it in spoilers in case anyone wants to read it, as it is kind of near the end. Great book btw.
Spoiler "We seem to have a miserable instrument failure, sir"
"What of it?"
"I'm reading 15,000 meters and still falling"
"That is foolish. There is no such depth"
The captain glared at a million yen's worth of equipment and thumped it
"Ah, sir. It is shallower already."
Beneath the thunders of the upper deep. As the *protagonist* knew Far, Far beneath in the abysmal sea, the Kraken sleepeth.
And now it was waking up.
Millions of tons of deep ocean ooze cascade off it's flanks as it rises.
"See" said the navigator "Three thousand meters already."
As it billows up through the icy waters it picks up the microwave noise of the sea, the sorrowing beeps and whistles of the whalesong.
"Er, one thousand meters"
The Kraken is not amused
"Five hundred meters?"
The factory ship rocks on the sudden swell.
"A hundred meters?"
There is a tiny metal thing above it. The Kraken stirs and ten billion sushi dinners cry out for vengence."
So, I was thinking there would be sudden darkness in the water below you. Not that Nordic waters will be particularly clear. I'm talking near jet black, even near the surface. If you ignore that, there could be a sudden swell as something below you stirs. You could only see that at the surface, though. So noise would also be important.
The only problem would be, why would you want to go out that far? The only reasons I could think of would be to visit a nearby island (Kraken could be sleeping close to the shore). Or the island could BE the monster. There could also be the promise of great treasure near where the Kraken sleeps if he is in the deep ocean.
EDIT: Or instead of the Kraken, it could be like the serpent J?rmungandr that Thor fights throughout the Norse mythology. It was a serpent that surrounded the Earth and would grasp it's own tail in it's mouth. In one of the stories Thor rows out to the deep ocean with a giant and nearly kills J?rmungandr by 'dual-wielding' his fishing rod and his hammer (the giant wusses out and cuts the line just before the death blow). Serpents are probably more in keeping with the dragon theme than the squid-like Kraken.