Druid Temple

The Druid Temple is an area that opens up after you defeat the 4 Elemental Guardians. The Master Druid is there, and he gives you 2 quests. The first one is to rescue the Princess from the Storm Giant in the Ice Palace. After that is done, a little later, he will lead you to this room where you must defeat the Spirit Guardian.

After that, you can switch alignments to Spirit, which you may need to do when going through Astral, Umbral and Spirit Planes.

You can also Soulbind your weapon, amulet, and rings here, and align your weapon with the Spirit alignment as well.