Just outside Tokyo, — one of the busiest, most fast-paced cities in the world — stands the “world’s best kindergarten.”

Designed by Tezuka Architects, Fuji Kindergarten in Tachikawa, Japan is an oval-shaped kindergarten where trees grow right through classrooms and kids are encouraged to run around freely throughout the open structure.

The main building is impressive enough, but it is also equipped with an annex with two more classrooms and some playing areas. Made of glass, steel, and wood, this extension is built around a 50-year-old Zelkova tree with a legendary story.

Once nearly uprooted during a typhoon, the tree was left dried up and lifeless. However, to the disbelief of locals, it eventually made a miraculous recovery and became healthy once again. The older residents recalled children playing on the Zelkova tree since even before the kindergarten existed, and it’s almost as if the tree came back to life to continue fulfilling its role as a play haven for the local kids.

Although the annex looks like it only has two floors, for the small children it actually has six, with some areas being just one meter (three feet) high. Takaharu Tezuka, the designer of the kindergarten said: “If a child is strong enough, they can reach the upper level without using the stairs. Other schools might not allow this, but the principal here believes children know their own limits. They stop when they have to stop.”

But just in case someone does take a tumble, all the outdoor areas are covered with soft rubber mats to cushion the fall.

Watch Tezuka’s TED talk for the full, fascinating background of this wonderful kindergarten.