Secret areas in first level

[Skoges]

I was able to get to the top of the platforms and to a couple of the islands that look like they aren't accessible. It seems to have just been a waste of time because nothing was in any of those areas except for a steam jump pad on one island. Am I missing anything? Are there any secrets to find in the first level?

[Radian]

There's some large flying creatures in the distance on one of them. You can shoot them but I don't know if there's a point to it.

[That1/30]

Some of the secret areas in the first level aren't entirely secret. The game can randomize the structure of the level to an extent. Like that one island off to the side away from the grove of trees. Some times a land bridge is there, some times not.
In some other levels a tunnel is open and some times it isn't.
There ARE in fact some secret areas that take some effort to get into. But I don't believe that there are very many at the current state of the game.

[LuckyN13]

Sometimes you find rare chests in those hidden upper areas, found one on stage 5 but couldnt afford to open it

[Xilo The Odd]

the stages have multiple configurations, sometimes you'll go over there and sometimes normal access will be cut off and typically nothing spawns over there.