She is the last population of the province Biscay, before entering Guipuzcoa on the oriental part of this one. Such a proximity situation, and the fact of belonging geographically to the basin of the river Deva, does that this locality includes, to many effects, in the Region of Low Deva, along with other municipalities of Guipúzcoa. With the nearby city of Éibar it forms the same urban plot. Ermua grew in the 60s and 70s to the shade of his neighbor and worked like a dormitory suburb of this one.

The municipality is composed by his city center and some quarters like those of Ongarai, San Pelayo, Onki zuri and Santa Ann. The quarter of The St Lawrence, which belongs to Zaldibar, is integrated urbanistically in Ermua. These quarters are very next to center and are part of the same downtown.

In Ermua he stands out for his harmony, the compound monumental set for the church and the palace of Valdespina:

'Palace of Valdespina', constructed in 1738 the second quarter of the XVIIIth century is a magnificent building residential of baroque style framed inside the baroque world of in refined and decorated version. It was realized by the architect Joseph de Zuaznabar.

'Parochial church of Santiago Apóstol' dates of 1600, it is the most beautiful Renaissance building. There is of the type of church of a ship of three stretches with high side chapels between the stirrups. Frenteando the ship there is, also, a chapel major narrower ochavada. (fte. to see the links and wikipedia)