Castellot of Mas Mateu Monument · el Montmell, Baix Penedès, Tarragona Image of el Montmell, not of the place itself. The Castellot de Mas Mateu, declared a Bien Cultural de Interés Nacional (Catalonia's highest level of heritage protection), is a medieval fortress in the municipality of el Montmell of which a ruined square tower survives, ten by ten metres in plan and with nine metres of height preserved, built of large, well-fitted ashlar blocks. Inside, remains of a dividing wall that split the space into two rooms can be seen. Photo: pere prlpz (CC BY-SA 3.0) What to see and do in el Montmell