Map showing the main monasteries in Ireland during the Early Middle Ages

From Early Christian Ireland, 1958 by Máire de Paor

"the settlement [Glendalough] was clearly a large one; a city by comparison with contemporary secular settlements, so that the compiler of the Martyrology of Oenghusin (9th century) could write in his prologue: ‘The cells that have been taken by pairs and trios; they are Romes with multitudes, with hundreds, with thousands.’

The little churches that were built in the monasteries have no architectural pretensions, but, as Leask says, ‘they have a special interest: they were evolve —unlike those of western Europe in the same period—in almost entire independence of Roman traditions of building’.

Two types of timber church are consistently described; a church of wickerwork or wattles, and a church of hewn timbers. None of either type still stands, nor have the traces of any been discovered by excavation, yet we have quite a good idea of what the early churches were like, since it seems that the first stone oratories preserved something of the form of their wooden prototypes."

De Paor on Irish Architecture

Important to remember when studying architecture of Europe, as noted in post above, Ireland, Scotland and Scandinavia were never conquered by Romans.Thus, a lot of stone building techniques and such never imported over until much later. So a lot of native architecture in non-Roman parts was some stone but mostly wood which has been lost to time.

Given climates, making things out of wood made more sense as stone buildings get very cold in the summer, let alone winter (hence Romans engineering Hypocaust systems that were available in Roman Britain).

So in these countries, when building from stone in the early middle ages became more common, you can get some unique features (like the Irish Round Towers). You can see evolution of it in Ireland comparing some of the early High Crosses with the later ones.

I seen a study before that Romans/Greeks developed such wonders due to the ready available materials for concrete making & the need for building stone buildings given their warm climates

If you check a map of active volcanoes in Europe, you'll notice the main ones are in Italy and Greece

And how was concrete making accelerated?

By adding volcanic ash to the mix and allowing it to set underwater, so it makes sense why Greeks and Romans were readily able to develop such marvels as their civilizations expanded and cultures heightened.

Final note - The long-term durability of Roman concrete structures has been found to be due to its use of pyroclastic (volcanic) rock and ash, whereby the crystallization of strätlingite (a specific and complex calcium aluminosilicate hydrate)and the coalescence of this and similar calcium–aluminum-silicate–hydrate cementing binders helped give the concrete a greater degree of fracture resistance even in seismically active environments. Roman concrete is significantly more resistant to erosion by seawater than modern concrete; it used pyroclastic materials which react with seawater to form Al-tobermorite crystals over time.

Description of a brawl breaking out at an Irish Volunteers meeting between Redmondites and what would be IRB types

Pearse punched some low energy Redmondite in the face and a Redmonite Priest priest challenged Ceannt to a gun duel lol

Another map of ecclesiastical sites founded by or associated with Irish monks during the 5th-12th centuries, many of these were the foundations for the Carolingian Renaissance during the reign of Charlemagne which British Historian Kenneth Clark states was the means which 'Western civilization survived by the skin of its teeth' during and after the fall of the Western Roman Empire.

Not a complete map though, as few sites on continent I can see not on it.

From Early Christian Ireland, 1958 by Máire de Paor

The noblest share of earth is the far western world
Whose name is written Scottia in the ancient books;
Rich in goods, in silver, jewels, cloth and gold,
Benign to the body, in air and mellow soil.
With honey and with milk flow Ireland’s lovely plains,
With silk and arms, abundant fruit, with art and men.

No fury of bears is there, and the Irish land
Never has nurtured the savage seed of lions;
There no poison harms, no serpent glides in the grass,
No frog harshly sings his loud complaint in the lake.
Worthy are the Irish to dwell in this their land,
A race of men renowned in war, in peace, in faith.

Poem originally in Latin by 9th Century Irish Saint Donatus, Bishop of Fiesole about his love for Ireland, which he misses. He is buried in the Fiesole Cathedral near Florence.

Painting is the 15th Century, Piazza Madonna by Andrea del Verrocchio showing Saint Donatus with John the Baptist with a Madonna and Child.

Map showing locations of High-Crosses that have figures carved on them

From Early Christian Ireland, 1958 by Máire de Paor