A much smaller but wealthier town than Pompeii, it was completely covered with 25m of volcanic ash in the AD79 eruption, as opposed to Pompeii's miserly 4m of ash. It lies much closer to Vesuvius than Pompeii and was largely evacuated at the time it was covered by ash.
Herculaneum was only rediscovered in 1709, when wells were sunk by locals. About 4 hectares have been subsequently excavated, with efforts now being expended on preserving the existing uncovered ruins rather than further excavations.
To this day, only 25% of the town has been excavated - The other 75% lies 50' under modern day Ercolano, under protective ash. But many tunnels have been built, revealing, for example, a large coliseum, a large plaza
It was originally a seaside town, with 300 skeletons found by the sea walls. They were thought to have died whilst waiting evacuation by boat. The eruption raised the land by 20m, so it now lies ~500m inland. But the original beach is actually still preserved. It is odd, looking at an old beach, deep underground, in a tunnel.
Everything is so much better preserved than Pompeii. The frescoes are more intact; the wooden beams and window frames are charred but still present.
A little bit of this is that the pyroclastic flows didn't destroy much. But mostly as the sheer depth of covering ash preserved everything well for nearly 2000 years.
This is one of the East-West streets (cardi), separating Insula I & II (Insula are blocks of housing). I like the paving slabs, not as rutted as Pompeii.