http://r2km7u25qebaefa7b6jdcjldymc2u337vzpx7ne773ypgs3qlq4xycqd.onion/index.php?page=PRIMER
This led me to: /8_1f0e3dad99908345f7439f8ffabdffc4/ CLI Terminal and Final Stage This page presented what appeared to be a command-line interface terminal. Clicking "EOF" took me to a terminal-like page. In the source code of this page, I discovered the final reference: 10_23693cff748o49r45d77b6c7d1b9afcd This led to the credits page, completing the challenge.