The Forgotten City

The Autisto steps listed above worked for me aswell. Thanks!

Finally managed to get it to unlock. The suggestions here weren't working for me but maybe what got it to work was after looping I talked to Galerius and got him to run and do some jobs for me, after he was done he talked to me and I explained that I was reliving the same day, he then told me the stories about Sisyphus, Tantalus, Ixion, and the Belide. Then I went around to all 4 statues and the achievement unlocked.

It seems you need to learn about the city being the Underworld before it pops. I had visited all 4 multiple times. Once I spoke with Equitia in the bathhouse it popped immediately.

You need to have at least met Equitia in the baths and have her tell you about the underworld. They don't need to be found in one run either.

I can confirm what Bondfan626 and Calex dEUS said. Once I met Equitia in the baths, the achievement unlocked immediately after unlocking the Bloodless Shadow achievement. I had already visited all four statues prior to this.

Again, confirming the above 3. As soon as Equitia tells you this (end of the long 'Common Thread' quest) it will pop if you've been to the other locations before.

One thing to note is the statues will turn to look at you. After looking at them if you turn away then turn back their heads will have turned to you. It sure feels like that’s part of “interacting” with them.

Thank you for the solution!

I had talked to Equitia again, after talking to enough people to get 3 different responses of what they remembered & she told me to meet her in the baths (I had already went to all 4 statues earlier). Upon talking to her in the baths, I got Bloodless Shadow, then after she mentioned we are in the underworld, Underworld Explorer popped.

I was having lots of trouble unlocking this today, decided to delete all my saves and start fresh on a new file. I went and grabbed a bottle of wine, got the accusatory note, the Apollo key and did Rufius and Vergil’s Quest, guided the Assassin into the shrine and saved Fabia, and then the 3 links and Bathhouse with Equitia. I only spoke with Horatio and the people in the Market Square for the links. After that, I stole the resin and looped, spoke with Rufius about the Roman Plaque and collected it. Once that was done I visited the statues in this order:

1: Wheel
2: Apple
3: Fountain
4: Rock

At that point it unlocked instantly, I think it may be an issue with it not tracking across exisiting saves, but that is every step I took to get it to pop first time.

Well I’ll be damned. I followed your directions (only made a minor change of getting the plaque in the same run without a loop) and it immediately unlocked without any issue. Thank you so much for this solution!