Alfheim

Alfheim is a world of untamed nature. A massive globe (several times the size of Earth) overgrown with millions of truly massive trees, the highest of them being close to one hundred kilometres tall. These trees make the entire world partially three-dimensional, with their massive branches (sometimes intertwined with each other, or connected with vines that are many, many kilometres long) housing entire cities.   There is a vibrant ecosystem thriving here, in fact a few of them on various altitudes. Things that do die tend to fall down (for many, many kilometres) before crushing down at the feet of these giants, where they are absorbed by the roots. Only a fragment of nutrition the trees need is gained that way, as majority is gained from sunlight of the several suns of Alfheim, which is then processed by the trees into massive amounts of nutrients (through some magically-enhanced biological proceses).   There are seven suns in the planetary system that Alfheim is a part of. They actually appear to be moving around Alfheim instead of the other way around, and there are no other celestial objects - they are also much less hot and bright than they should be given their estimated surface temperature and size (according to their sizes alone Alfheim should be a scorched desert). The stars behind them appear to have some form of a cycle, with periodic alterations that make it rather obvious that whatever they are they are not stars as understood by Mankind.