In order to find the Hellforge in Diablo 2: Resurrected, you’re going to have to explore the River Of Flame, which is accessed via the City of the Damned. But finding the way into the City of the Damned can be difficult thanks to a quirk in the mini-map. Diablo 2: Resurrected is a very faithful, er — resurrection of the original game, so many minor niggles like this one haven’t been removed.
Starting at the Pandemonium Fortress, head into the Outer Steppes and explore until you find a staircase leading to the Plains of Despair. The staircase leading to the City of the Damned will be somewhere on the outer border of the Plains of Despair.
The reason players sometimes can’t find it is that the mini-map marker for the staircase is displayed outside of the border for some reason. This means that unless you’ve passed very close by to it, it won’t show up on the map. As a result, many players see that the outer border of their mini-map is complete, and think that means they must have searched everywhere.
To ensure this problem doesn’t happen to you, stick very closely to the outer border of the Plains of Despair, systematically circling the edge until you spot the staircase. It’s not that easy to see until you’re pretty much right on top of it.