Or perhaps the Kaiju (ex. from Pacific Rim) generate at random (in a repeating cycle, without replacement until the end of the cycle) in Switzerland and the Seven Islands (Iceland, Ireland, Corsica, Sardinia, Sicily, Crete, and Cyprus). These eight territories remain impassable to ordinary units, but the monsters can spring out without warning. Kaiju are amphibious for movement, attack and defend with a strength of two, and leave supply centers devastated for a game year after their departure.
Or the Kaiju are secretly controlled by players, each player getting to launch a Kaiju at a time and location (the 7 islands or Switz) of their choice in 1902 or later. Kaiju can be supported as well as attacked, and may fight or support each other. The launching player also gets to name their Kaiju.