The original Taco Bell building has been ripped out of the ground for safekeeping. In 2015, the first ever Taco Bell restaurant was uprooted from its original location in Downey, California, and driven down interstate 5 to the Taco Bell HQ in Irvine, CA. Since then, it's been kept in the rear parking lot of the Taco Bell HQ, where it lies on a raised platform, empty and locked up. This relic isn't technically open to the public, but it isn't guarded either, so visit at your own risk.
From Atlas Obscura:
"To get to the parking lot where the building is located, take the front entrance road at the Taco Bell headquarters and follow a counter-clockwise loop around the parking garage. Please be discreet, be respectful, and don't touch or try to enter the building. Be aware that the building is occasionally fully covered with tarp to protect it from inclement weather, so it may not be possible to see it if it's been raining."
