I first learnt about this Church from reading a book about the Beuron School of Art (I believe the book is still in print, and I obtained it with little difficulty by ordering it through a local bookshop), which made a reference to St Gabriel's as being important because it is the most complete, surviving work of Desiderius Lenz, the monk who is seen as the founder of the Beuron School. It was a conversation about this Church that prompted Zero to comment, "Well, let's go to Prague then", though is is probably overstating things to say that it was the purpose for our going.
I first encountered the Beuron School when I visited the Abbey of St Hildegard, Eibingen, during a visit to my parish's twin parish in Germany. The guided tour of the Church on the Abbey website gives an excellent first glance at the Beuron School and its implementation at St Hildegard's. Do explore the whole tour, as it is catechetically and Liturgically superb. There is quite a technical understanding of the principles of the Beuron School - a relation to Egyptian representation of human figures, a complex geometric rule for the representation of male and female figures that is explicitly linked to what we would now talk about as male-female gender complementarity in Adam/Eve and in Christ/Mary - but it is not necessary to follow all this in order to appreciate the work of the Beuron School.
I next encountered it during a visit to the Abbey at Monte Cassino. The crypt, particularly enshrining the tombs of St Benedict and St Scholastica, is decorated in the Beuron style. A good account of the crypt, including pictures can be found here.
According to Wikimedia:
Church of Saint Gabriel (more precisely Church of Annunciation) and adjacent abbey in Prague-Smíchov (in Czechia) were built at the end of the 19th century and belonged to the Order of Saint Benedict. In 1919, after the declaration of Czechoslovak Republic, Benedictine sisters left for Austria and sold the buildings to the Czechoslovak Ministry of Postal Services. In present, both the church and the abbey belong to Czech Post.
Though the photographs may make the Church appear bright and well maintained, I am not sure that substantial effort is being made to preserve the paintings. Some of the paintings, particularly in the nave, appeared to be darkened and faded. I haven't been able to find anything in English on the web, so herewith some photographs, either scanned from post cards, found on Czech sites or taken myself. If I have time, I will try to post more about the Church later.
This full picture is taken from a post card, and makes the paintings look much brighter than they are now. The grille that you can see on the right is also no longer there, but the arrangement of the high altar has not been changed. I loved the image of the Father in the apse (the text either side of the image reads "I am who am", though you can't see it on this picture), so that, offering Mass at the altar, there is a real representation of the offering being made "to the Father". Over the arch you have the Lamb, standing above the new Jerusalem with its towers and four streams of life; the saints in their white dress approach offering incense in adoration of the Lamb. The text beneath reads: "Blessed are they who have washed their clothes in the blood of the Lamb". This, and the many other images of saints in the Church, gave a real sense of the Liturgy being a presence of heaven on earth
This is my own photograph of the sanctuary as it was for Sunday Mass. You can see the angels around the side of the apse - giving a real sense of a Liturgy that is first of all a heavenly Liturgy, and then a Liturgy that is celebrated on earth.
These two statues, of the Angel Gabriel and the Virgin Mary, face each other across the Sanctuary - you can see them in the photograph above. They look strikingly modern - particularly the stance of the Virgin - but I think they date from the same time as the decoration of the Church. On the column beneath St Gabriel you have the words "Hail, full of grace" and beneath the Virgin Mary "Behold the handmaid of the Lord" - and this represented across the altar at which, during the celebration of Mass, the Lord again becomes flesh under the forms of bread and wine.The most striking image in the Church is that of the Virgin Mary, Seat of Wisdom. This is behind the high altar, beneath the painting of the Father in the apse. It can be seen from the nave, framed by the four columns that support the baldechino over the altar.
St Joseph blurred a little bit, I am afraid, but I have to put him in!