It is very beauiful inside, the cupola is frescoed with such a richness of color and design. The skull of 13-year old Saint Agnes is also at rest here (while the rest of her body is elsewhere).

She was ultimately beheaded in an arena/stadium during the Domitian rule in 5th century AD. The previous plans for her martyrdom were foiled by the higher levels than the Roman henchmen Domitian employed.

This is a Baroque church. The exterior is pure white and it has a concave front facade. Ornamentation outside is at a minimum and it is situated pretty much in front of the Four Rivers Fountain. The interior has an abundance of marble detail in many colors.

This Church faces onto one of the most complete piazzas in Italy. It s a stunning piazza and this church is another example of brilliant craftsmanship. Please respect the church once you're inside. Nearly all the tourists visiting this church when I was there, entered and then proceeded to walk around taking pictures ignoring the No Photo signs and dress code.
If you visit churches then respect them.