The stone paths curl around the lakes and exit to the top. It is presumably the hardest beginner track in btd5. A set of 2 lakes with a stone path between them. This is one of the easiest tracks in btd5. No matter the version you choose, Bloons TD 5 is the best of the series.
But there's a larger variety of content than you'll find in Cities and Battles, and ultimately it's the best singleplayer option out of them. It's still solid and gets updated a few times a year like the other versions, and really it's not lacking much if you're just in it for the core gameplay.
It might not be the flashiest or most fleshed out of them, but it got to be one of the most beloved flash games out there for a reason. The flash version is definitely best for new Bloons players or anyone trying to play at school or work. The mobile version is prime if you're never home or at a computer.