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View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
Planets generally orbit their stars in a roughly flat plane because they formed from a protoplanetary disc, a flat disc of material surrounding a young star that is leftover from the star's formation. The material in this disc is rotating around the star, and when planets form from this material, the angular momentum is conserved and the planets continue to orbit in the direction the disk was rotating.
It's not all 100% flat though, even within our own solar system. In fact, none of the other planets orbit in the same exact plane as the Earth. The inclination of their orbits vary from planet to planet, but most are only tilted by up to a few degrees relative to us, except for Mercury which is tilted about 7 degrees, and Pluto which is tilted about 17 degrees.
As to whether you would find anything if you travelled "up", and here I'm taking up to be perpendicular to the planet of the Earth's orbit, you would not find another planetary body in our own solar system, and it would likely be very rare to find one in other systems as well. I suspect it would involve two planet sized bodies impacting each other in such a way as to change the orbital inclination by a large amount, without destroying both or destabilizing the orbit. If we are talking about things other than a planet though, then yes, there is plenty of stuff up, even in our own solar system. Search up on the Oort Cloud for an example.
There's nothing here!