I am trying to convince a friend to pick this game up from here, and he asked me how many levels there are, can someone remind me how many levels in grimrock there are?

I asked that earlier and the answer I received was

spoiler

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13.

But they're pretty time consuming to get through, at least the first run.

Ah yes thanks.

I know they are most people have clocked the game in at 10 hours or so, which is longer then the average modern game length 6 hours

It took me around 16 hours to finish it in normal difficulty, with 62/71 secrets and 5/7 treasures. It would have taken me a bit longer if I had been able to backtrack from level 10 to complete a couple of extra secrets, though.

Edit: I couldn't backtrack because I didn't find a particular button to open a wall, not because the game doesn't allow you.

Huh, I've four hours on my belt yet and I'm on level 4. And I mean EASY. ;)

I'll probably need more time for higher levels, so I guess anything between 15 and 30 hours in my first run is possible.