the Pope crowned him Imperator Romanorum ("Emperor of the Romans") in Saint Peter's Basilica (wiki) - in 800

Charlemagne's Palatine Chapel both uses San Vitale in Ravenna as a partial model and inspiration and incorporates materials taken on Charlemagne's orders from Ravenna . "Charlemagne visited Ravenna three times, the first in 787. In that year he wrote to Pope Hadrian I and requested "mosaic, marbles, and other materials from floors and walls in Rome and Ravenna, for his palace" ... The Chapel of San Vitale makes use of ancient spolia conceivably from Ravenna (Einhard claimed they were from Rome and Ravenna), as well as newly carved materials." Wiki (Einhard was a servant to and wrote a biography of Charlemagne)

...was founded around 775, probably on the orders of Charlemagne. (AB Ev.)

Palais du Tau holds the "Talisman of Charlemagne", buried with him at Aix-la-Chapelle, in 814, and re-discovered when the tomb was opened by Otto III in 1000. The talisman was then preserved in the treasury of the Reims Cathedral.
See traveltoeat.com

"The "Historia Caroli Magni" tells of how "[a]t the request of Saint James who appears to him in dream, Charlemagne embarks on four wars to wrest Spain from the Saracens. In the first war, he takes his army to Santiago de Compostela and conquers all of Spain. (...) Once the last Saracen leaders are defeated, Charlemagne invests Santiago de Compostela with considerable powers and begins the return to France."
See en.wikipedia.org

The church of Santo Stefano was established by Charlemagne in the 9th century. (Wiki)

He was buried in the Cathedral (814). He also began the construction of its Palatine Chapel around 796.
See en.wikipedia.org

Basilica of Saint Severinus: a legend surrounding the basilica is that the olifant of Roland, nephew of Charlemagne, famous for his death at Roncevaux, was placed on the altar of the Saint-Seurin basilica by the emperor bringing back the body of the valiant knight. The famous Song of Roland also refers to it.
See fr.wikipedia.org

According to tradition, Sant'Antimo Abbey was founded in 781 by Charlemagne in response to a grace received: the emperor and his troops had been spared from the plague that was raging in the region, during his return journey from Rome, where he received from the Pope the bodies of Saints Antimo and Sebastian. (Nomination file, p. 86) The foundation by Charlemagne is almost certainly to be interpreted as a pure medieval legend
See it.wikipedia.org

According to a tradition, the abbey Saint-Jean de Sorde was founded by Charlemagne. (Nomination file) - The Historia Caroli Magni (or (Pseudo-)Turpin Chronicle) states that the Saint-Jacques-de-la-Boucherie Church, of which the Tour Saint-Jacques is a vestige, was founded by Charlemagne. However, historians have never been able to verify this.
See fr.wikipedia.org

In the St. James Chapel of the Basilica of St. Anthony of Padua, the frescoes show "Charlemagne's Council, which contains actual portraits of some of the most significant figures associated with the Carraresi court (...) and a portrait of Charlemagne himself; this latter shows a clear resemblance to emperor Louis of Hungary, an ally of the Carraresi rulers of Padua. The entire image is, therefore, a clear political statement of the prestige of both the lords of Padua and of the Lupi family." (Nomination file, p. 121)

Brescia, San Salvatore: "The monastery is traditionally considered the place where Desiderata, wife of Charlemagne and daughter of the Lombard King Desiderius, spent her exile after the annulment of her marriage in 771."
See en.wikipedia.org

Charlemagne conquered Florence in 774 and the city became part of the March of Tuscany.
See en.wikipedia.org

In 774, the Frankish king Charlemagne, after defeating Desiderius, the last king of the Lombards, donated the city of Ferrara and its territory to the Holy See.
See it.wikipedia.org

Linz (ID No 13a/b): In 791 Charlemagne and his army passed Linz on a campaign against the Avars. In 799, the Emperor gave St. Martin's Church and its castrum to his brother-in-law Gerold as a fief.
See de.wikipedia.org

He was present at the consecration of the monastery church