The Cliffs of Moher

[Doireannjane]

Secondly, I’ll also bring your attention to McDermott's castle in Lough Key which has the same very, very particular attributes depicted in the Voynich.

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McDermott's Castle is a castle and protected national monument located in County Roscommon, Ireland. The site of a fortification since at least the 13th century, the structure's tower house may date from the 16th century, with much of the current building (including its crenellations) dating to the 19th century.

I guess it makes appearance of that castle in VM not very probable.

Yes if you continue reading.. it was rebuilt because of destruction. Note the "may date from" in the one single sentence you selected from all of this. Recreation happens a lot with castles. It describes the multiple recreations (not additions/changes) that were made and added throughout the centuries. 

By the early 19th century the castle was in ruin, until architect John Nash was commissioned to redevelop the structure as a summer house or folly.[7][8]

A rebuilt castle featured in the final part of the 1235 conquest of Connacht by Richard Mór de Burgh, 1st Baron of Connaught. The castle came under siege, first by a raft-mounted catapult, and then by fire ships. Cormac MacDermott, King of Moylurg, was forced to surrender. (wikipedia)

There was absolutely a castle standing tall there in the 1400s. Unfortunately no photos.