Gensokyo is the land that lies parallel to our world, you can't reach it from the outside unless you reach your full spiritual connection with the universe and kill yourself to become a Youkai (ghost). So to make understanding this easier, Gensokyo is in the real world but an illusion to anyone outside the barrier in the outside world. Gensokyo inhabitants can access our world through portals.
Gensokyo has a great barrier placed on it (seen in the photo) which protects it from being accessed from the real world. It exists in the real world on Earth but you can't see it, so even going there in the real life nothing would happen. This is where all the spiritiual and ghostly spirits from the world come from.
"Gensokyo was originally a desolate, haunted region of Japan ages ago. The youkai that lived there began to terrorize the surrounding lands, because of this, powerful and heroic humans were sent to exorcise and exterminate them. As time passed, the technology and population of humans increased greatly, which lead to an increase in human influence. Due to this, Yukari Yakumo implemented a plan roughly 500 years ago to restore the power of youkai in Gensokyo by creating a "Barrier that divides Reality and Fantasy" (the plan was called "妖怪拡張計画, "Youkai Expansion Project"). From that day, Gensokyo became a place where it brought in things that have become fantasy outside; in other words, things that were forgotten in the Outside World such as youkai, lost items, and such are transported into Gensokyo.[1] It's said that it's hard for things that have become fantasy to leave Gensokyo, but beings that are powerful enough possesses the ability to leave Gensokyo at their will. In 1885 A.D., Gensokyo was sealed off from the increasingly scientific world once again with the creation of a second barrier, which was called the Great Hakurei Barrier. There has been little contact with the outside world ever since. It's known that the language spoken in Gensokyo is modern Japanese"
Yukari is one powerful such Yokai which sealed of Gensokyo. "Gensokyo exists roughly parallel to the real world. As the inhabitants of Gensokyo, however, have developed their spiritual lives instead of following the trend of technological advancements in the real world, Gensokyo itself can appear to be a Japan from hundreds of years ago."
So, if you want to live in a magical wonderland filled with hot yokai women, you should kill yourself. This is true btw.
