Cairn na Burgh Beag is the smaller of the two "Carnburgs" (as they are nicknamed) at the northeastern end of the Treshnish Isles in the Inner Hebrides.

However, an unusual feature of the castle is that its defences straddle both islands: There is a small guard-house and a well on Cairn na Burgh Beag.

[5] Both of these grassy islands are remnants of ancient lava flows, and both have a distinctive profile: They area flat-topped and trimmed with cliffs.

In 1343 there was a reference to the castle of Iselborgh, which was granted by David II to John of Islay, Lord of the Isles along with Cairn na Burgh Mòr and Dùn Chonnuill in the Garvellachs.

[6] Duncan and Brown concluded that Iselborg "certainly lay, with Cairnburgmore, in the Treshnish Group"[7] and in 1980 the RCAHMS also believed that "there appear to be good grounds for accepting the view that Isleborgh is an early name" for Cairn na Burgh Beag.