How many levels long is this game?

It's been years since I played. The single-player part of the game has 5 chapters, each with a couple dozen levels. But most of the levels are fairly quick to do and you don't have to do all of them to get to the next chapter. How long to beat says it usually takes about 7.5 hours to finish the solo part of the game, but it can be rushed in 3.

So it's firmly in the "medium length" territory. Not too time consuming but if you play maybe 5 or so levels per sitting you end up getting a lot of mileage.

I just started up the game (haven't played since I 100%ed the solo part back in 2012) and didn't bother counting the levels, but I see that I have earned 116 keys from beating levels, which probably means that's the number of levels there are. There is also a co-op mode with plenty of levels of its own, but that's not needed for the main story.

Oh man. I remember getting this when it landed here in that cheap indie bundle when GOG was still starting out with expanding their catalog. Fun little game. :)