Within the Muskiz area is the most emblematic and important urban centre, the result of its splendid mining past. Founded in the year 1877, it conserves its original character, which we can see through the wooden houses of the workers (some of which have been refurbished), the mining unions, the grocers shop, and the most important mining hospital in the area, which was recently pulled down.
The population of the upper part of the valley, such as La Arboleda, Triano, El Sauco and numerous other districts, with their 5,060 inhabitants, exceeded, in 1901, the population of the lower valley area of Trapaga-Trapagaran, which then had 1776 inhabitants.
Next to La Arboleda/Zugaztieta is a chaotic landscape, of rare beauty, with its pond known as El Ostión, next to which is a recreational area. Next to Las Cármenes well is the Blondies mine and, further on, close to the main road, Parkotxa pond, a former mineral washery which is now used to teach angling.
In the Interpretation Centre of Peñas Negras we can find photographic documentation of the La Arboleda/Zugaztieta area before the mining boom.
Throughout the Zugaztieta/La Arboleda area numerous different open air activities can be carried out: strolls, hillwalking, climbing, riding and mountain biking, making full use of the infrastructure of the former pathways which were constructed to exploit the mines.