From my research, these seem to be particularly in evidence within Northern Europe where they are called "Sacramentstoren" or "Sakramentshäus".
Archdale King has this to say of them in Eucharistic Reservation in the Western Church:
The elaborate stone structure in which the Eucharist is reserved in many of the churches of Germany and the Low Countries, isolated from the altar and normally on the gospel side of the sanctuary, is known as a sacrament house. They were often sculptured in the form of a monumental tower, approached by several steps, and with a railing around, on which candles were placed. Sometimes, also, there were two or more storeys and a space above for a light.
These sacrament houses appeared first in Germany in the fourteenth century (c. 1380), and became increasingly popular both there and in the Low Countries in the two subsequent centuries.
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Sacrament houses are found also in France, although they are comparatively rare.
Here are some images of Sacrament Houses.
Sint-Pieterskerk, Louvain, Belgium. 1450
St. Jacques, Louvain, Belgium. 1539. Note the prickets on the railings for candles.
Cologne Cathedral, ca. 1460 (Image source)
Münster in Heilsbronn, 1515 (Image source)
St. Martinuskerkaalst. This one has more of a classical style and reredos appearance to it.
St. Lorzen, Nuremberg, 15th century
Here, as well, are some modern day examples.
St. Stanislaus Kostka Church, Maspeth, New York
Cathedral of the Madeleine, Salt Lake City
