Ancient Rune

First, check the style.css file and look at the binary string in the top comment:

01100001 01110010 01100011 01100001 01101110 01110101 01110011

Converting it from binary to ASCII gives arcanus. Click the golden keyhole on the gate, enter arcanus, and unlock the next stage.

Inside the cavern, inspect the page source and find the path containing the coordinates 100 101 112 116 104. Converting these ASCII values reveals the first rune: depth.

Next, go to Chamber III and inspect the grout color variables:

#5f6368, #616d62, and #65725f

Converting the hex bytes to ASCII gives _chamber_, revealing the second rune as chamber.

For the final rune, click the Diglett in Chamber II. This reveals the key 83 in the console. Open the console and run:

awakenCave("Chamber of Shadows", 83)

The output reveals the final rune: treasure_8a9f3.