The dedication is to St Philip Neri.
This chapel is in the territory of the diocese of Porto Santa Rufina.
Olgiata is claimed to be the highest-class suburb of Rome, and it is certainly the wealthiest. As is rather typical of such places, finding your way round can be difficult owing to security concerns and a lack of proper addresses. Online maps have been putting the chapel in the wrong place.
The "streets" (actually, each is a complex of streets leading off each other) are simply labelled with letters of the alphabet. The chapel is on the left hand side of what Google Maps claims is an offshoot of "Strada H" acting as the driveway to the old villa of Castello dell'Olgiata.
To get here (in theory), use the rather complex Olgiata junction on the Via Cassia, and find the roundabout (gyratory) on the west end of it which is called the Largo Olgiata. Go straight ahead on Strada B, bear right at a second roundabout, take the second left, turn right at the crossroads and the chapel should be on your left.
However, the suburb is allegedly a "gated community" with access monitored 24/7 by a security company. This kind of paranoia is unusual in Italy.
The Castello is a country villa on the site of a mediaeval farmstead which probably had a chapel, as many others in the Roman Campagna did (some survive). This was allegedly turned into a genuine castle or castello by the Orsini family in the 15th century, by the provision of a curtain wall on a rectangular plan with four corner towers.
The farming estate attached to the Castello was bought by the Milanese banking family of the Olgiati in 1566, hence the name. They sold out in 1645, but the name stuck.
In 1744 the Chigi family obtained the property, in the person of Agostino Chigi della Rovere who had become head of the family in that year. He ordered the Castello to be remodelled as a grand country villa, which was laid out on a symmetrical plan. As well as the usual private villa chapel within the premises, a little public chapel was built next to the villa approach driveway just before the carriage turn. This chapel deliberately spoiled the symmetry of the complex.
The positioning of the chapel demonstrates its originally public character, and its size the paucity of the local population. The mother church was then San Pancrazio alla Isola Farnese.
The estate was let out as a tenuta (tenancy) during the 19th century, but was undeveloped when sold in 1930 to Mario and Clarice Incisa della Rocchetta, who were to be a long-lived couple. In their youth they oversaw a thorough makeover of the estate and its buildings, and founded the Razza Dormiello Olgiata which became an internationally famous race-horse stud farm.
The revitalisation project included the chapel, which was restored by Clemente Busiri Vici in 1933.
In 1950, the new parish of Sacri Cuori di Gesù e Maria di Porto Santa Rufina was inaugurated at La Storta but apparently Olgiata with its chapel stayed with San Pancrazio.
Clarice Incisa della Roccetta initiated the development of the private suburb in 1961 via a company called L'Olgiata Romana S.p.a. The layout was substantially completed by 1968, and included a very prestigious golf and country club which is now of the highest standard after a necessary revamping in 2012.
The last public Mass celebrated here that the writer has been able to trace was a Sunday Mass for a Filippino expatriate community in the zone of La Storta from 1984 to 1986.
In 2014, the suburb received its own parish church of Santi Pietro e Paolo all'Olgiata.
This small and delectable late Baroque (tardobarocco) building stands on its own on a lawned area flanking the Castello driveway. It has two separate architectural elements, an almost square nave and an octagonal domed sanctuary.
The fabric seems to be in brick, but is entirely rendered in a very pale orange render which looks in good condition.
The nave is a very short rectangle, almost square, and has a gabled and tiled roof. Each of the three exposed sides is dominated by a shallow rectangular recess, into which is fitted a blind arch with very thin pilasters and archivolt. The side walls, slightly longer than the width of the façade, each have the recess flanked by two very thin vertical grooves not reaching ground or eaves. These walls have a simple roofline entablature consisting of frieze and cornice, and each has a single square window.
The façade arch contains the single entrance doorway. Unlike the side walls, there is no crowning entablature. Instead, the lower bead of molding of the side wall entablatures is carried across it as a string course, creating a false pediment fitting into the gable. On the tip of the gable is a very small bell-cote for a single bell. Over the doorway is another false pediment, being a triangular panel in a broad frame with the side corners cut off.
Oddly, the nave is slightly wider than the near side of the octagonal sanctuary which it abuts.
The sanctuary has a roofline frieze and dentillated cornice. On this sits the low octagonal dome, in grey fish-scale tiles covering eight curved sectors separated by very thin ribs.. There is no drum or lantern.
Each exposed wall has a square panel below the roofline, with a thick blank frame. The ones in the diagonal sides contain windows. The cardinal sides each have an empty round-headed statue recess below the square panel.
The interior is apparently richly frescoed.
The chapel is within a "gated community", and there is no information online about who is responsible for it, or who holds the key.
If you wish to play golf at the Golf Club, for which you need to book, you can detour to view the chapel exterior.
The lawn around the chapel is very well maintained. There is no path, which is good evidence that the edifice is rarely open and little used.
"Venetouno" article on the golf club (contains only online photo of chapel)