If you're talking about an early quest, I think it's the culture bldg: 'Ancient Runes'. You find it under the culture tab of your build menu. On browser, mine's on page 2. I've never tried to build anything on the mobile app, but it should still be early in the listings; mine's the 9th culture item in that tab.
Players have campaigned to get the name of that bldg changed with no luck. It's incredibly confusing considering we have Ancient Wonders that are filled with runes. This question comes up every so often; you're definitely not the only one it has confounded!