As far as we know , Herculaneum  was an italic city founded around the IVth century B.C. coping, in the geometric regularity of his structures, the lay-out of Naples, to see how the "decumani" (the main streets, with an east-west orientation) and the "cardines" (narrower streets) identify with those of the Partenopean city.
There is  undeniably a "feeling" about Herculaneum which is quite different from what one "feel" in other ancient world centres brought to light so far, including Pompeii.
To a large extent this is due to the special circumstances of its interment by Vesuvius during the eruption of 79 A.D. 
The city was not struck by ashes and lapilli, but by a torrent of mud flooding down from the slopes of the volcano. Having solidified and becoming tufalike, it constituted for centuries the best possible defence  against atmospheric agents and against illegal excavators.
Towards the end of the first century B.C. the town become a resort center for the Roman aristocracy. Unlike Pompeii, Herculaneum seems a more peaceful town, especially devoted to navy and fishing with a lot of greenery and vineyards. It is said, in fact, that Herculaneum was Epicure's favorite place for his philosophical studies. 
Herculaneum had four to five thousands inhabitants and its square measure was a fifth smaller that of Pompeii.
It was destroyed by the 79 A.D. eruption.
Herculaneum seems more elegant and refined than Pompeii because of the original character of architecture and decoration (ornaments) and because of the natural position above the scenary of the gulf.
Excavations began in 1709, while from 1738 to 1765 systematic explorations were conducted by order of Charles III of Bourbons.
From 1927 the excavations in the open of the whole area were begun by Amedeo Maiuri.
 

The Casa d'Argo (Argus'House) with two floor, a garden surrounded by a  portico with columns;

The Casa dell'atrio a mosaico (House with a mosaic atrium) large  edifice with a  'tablino' (living room), a garden,
terraces and some halls with rich paintings;

The Casa del tramezzo di legno (the House with a wood partition) with a huge atrium decorated with frescos;

The Casa Sannitica (the Sannitic House) a kind of pre-roman construction with a wonderful atrium and some rooms with  fine frescos ;

The Terme (the thermal baths) divided in male and female, a huge complex of gymnasiums, dressing-rooms, swimming pools and some halls with mosaic floor;

The Casa di Nettuno e Anfitrite  (the Neptune and Amphitryte's House) with a nice nympheus covered by a colourful mosaic . This house shows us a shop with amphorae that is the best preserved shop of the ancient world;

The  Palestra (the gymnasium) with big halls closed by porticos and a large basin with a beautiful bronze fountain;

The Casa dei Cervi (the deer's house) a rich edifice with an atrium and a triclium  , in which  we can admire the wonderful marmorean group of deer assailed by dogs; many halls, in which of one with red walls with the strange statue of the  Satiro con otre (the Satyr with a wineskin); 

The  Casa del rilievo di Telefo (the Telefo's relief House) a very smart construction with a atrium, some halls in which of one there is the most luxurious marmorean decoration of the ancient world;

The Casa della Gemma (the jewel's house) painted in red and black, in the kitchen there are the crockery still on the hearth;

The Casa dello scheletro (the skeleton's house), so called because the skeleton founded during the excavation ;

The Terme Suburbane (the suburban thermal baths) with no difference between male and female sectors , with  a fountain sormounted by an Apollo's statue in the atrium, a big swimming pool.