What is the ruling on contemplating God's creations—such as the sky and trees—with a purely worldly intention of reducing stress and increasing focus, without intending it as an act of worship?

Reflecting on the creation of the heavens and the earth with the intention of inferring Allah's greatness and power is among the greatest acts of proximity to Him. One who does so without this intention misses out on the reward but does not commit anything forbidden. As for looking at the sky for recreational purposes, it is permissible and there is no harm in it. Jurists have explicitly stated the permissibility of traveling for leisure and sightseeing.