Herod accomplished marvels in architecture, dwarfing even some sites in Rome. While Jerusalem shrank in population in the Second Temple Era after the deportations, it expanded hugely under Herod. Herod's political brilliance is revealed by his ability to navigate between Jewish sensibilities and Roman rule. He was an excellent middleman. Herod knew that if he were to be successful as king of Jerusalem, he had to maintain the sanctity of the sacred precincts of the temple -- especially considering Pompey's behavior.
Herod built a huge complex on the eastern hill that would dwarf any of his predecessors' constructions. Herod rebuilt the temple in a classic Greco-Roman style temenos with a huge open-air temple porch area, within which was a shrine. It was twice the size of the Roman Forum, with some stones over 12m long and weighing hundreds of tons. However, the eastern hill was not big enough. Thus, he had to build artificial support to level off the hill and build his structure.
Rulers wanted to live on the western hill, which is higher than the eastern hill, and received the cool Mediterranean breezes. They wanted to connect the western hill where they lived and the temple mount. There was a big bridge for this purpose.
Within the temple was the ritual bath. One had to bathe in the mikhva after partaking in the everyday non-sacred realm, after activities such as sex or childbirth which are not sinful but not sacred either, before worshipping in the temple.
A Roman may view the whole temple complex as a temple in the Greco-Roman style. However, within the courtyard was what a Jew would view as the actual temple. There was a balustrade, a sorag, past which a non-Jew could not proceed; there is the balustrade inscription, a warning about not crossing the balustrade. Since the balustrade was not in the original temples, it is among the innovations of this new complex.
Herod also built the Antonia Fortress on the northern side of the temple mount. This not only served to protect the vulnerable northern side, but also allowed him to oversee what was happening on the mount. Herod, like the Romans, always wanted to protect what was happening on the temple mount because if a revolt were to happen then it would arise on the temple mount. During the harvest pilgrimage holidays, on the one hand the holidays are an economic boom since countless people come to Jerusalem to make offerings to the temple. However, they also rekindle nationalistic sentiments and remind somebody of the glory days when Jews weren't under foreign control. The Jewish population at this time would far outnumber the Roman population and the Antonia Fortress helped Herod to keep the upper hand.
The wailing wall or western wall is the western facade of the temple mount complex, not the temple itself.