This article was originally published on Atlas Obscura as "Five Architectural Easter Eggs Hiding on Gothic Cathedrals."

The modern use of the term “easter egg”—not the holiday treat but rather a hidden joke or surprise item inserted in a piece of media—originated with Atari in 1979, when a developer snuck his name into a game hoping to get some recognition as the creator. But these surprise treats, hidden to all but those who look closely enough, aren’t only lurking in the digital world. Some of the best easter eggs are snuck into the physical architecture around us.

The excellent thing about architectural easter eggs, be they tongue-in-cheek, carved out of spite, or simply placed as a fun treat awaiting an observant eye, is that they endure in the landscape around us, becoming a sneaky and often confusing part of history. Here are five hidden carvings that dot historic structures with a bit of human nature.