As a quick DuckDuckGo Search for "searchguide.level3.com" reveals, this is a malicious site and there is lots of malware out there that makes your browser or system redirect web requests to their site.
As you say this redirection does not happen with other browsers or a temporary Chromium profile, my guess is that only your normal Chromium profile got infected. Maybe you find some suspicious add-ons in the
chrome://extensions/ Extensions tab, but it's also possible that the infection is hiding itself and sitting somewhere deeper.
Therefore I would personally recommend to nuke all your user's Chromium profile and settings and let it recreate them the next time you start it. Maybe you want to export your bookmarks and write down your stored passwords somewhere before that.
To delete all your user's Chromium profile and settings, exit all Chromium processes and then remove these two directories:
Additionally, as just deleting the user profile has not worked on the first attempt, you can purge the whole
chromium-browser package and clean all its global configuration as well, and reinstall it again afterwards. To do this, run:
sudo apt purge chromium-browser
sudo apt install chromium-browser
Next time be more cautious when you download stuff or visit shady links.