"The Interior Castle Or The Mansions" by St. Teresa of Avila (16th Century)

Full book link: https://archive.org/details/St.TeresaOfAvilaTheInteriorCastleOrTheMansionsIncludingSomeOfHerMoreInterestingLetters/page/n25/mode/2up

1900s Catholic encyclopedia biography: https://www.newadvent.org/cathen/14515b.htm

via Wikipedia "Teresa of Avila" entry:

The Interior Castle, or The Mansions (Spanish: El Castillo Interior or Las Moradas), was written in 1577 and published in 1588.[32][33] It contained the basis for what she felt should be the ideal journey of faith, comparing the contemplative soul to a castle with seven successive interior courts, or chambers, analogous to the seven mansions. The work was inspired by her vision of the soul as a diamond in the shape of a castle containing seven mansions, which she interpreted as the journey of faith through seven stages, ending with union with God.[34]

Fray Diego, one of Teresa's former confessors, wrote that God revealed to Teresa:

... a most beautiful crystal globe, made in the shape of a castle, and containing seven mansions, in the seventh and innermost of which was the King of Glory, in the greatest splendour, illumining and beautifying them all. The nearer one got to the centre, the stronger was the light; outside the palace limits everything was foul, dark and infested with toads, vipers and other venomous creatures."