Oldofredi castle, one of the oldest and best preserved in the Brescia region, is located on a rocky foundation in the southern part of the historical centre. It is accessed by two entrances in the north and east, where in the 1980s a massive staircase was built. It stands on an area inhabited since Roman times and the first mention of a castle in Iseo is contained in the Altarpiece of Santa Giulia (St. Julie), a list of the properties of the Brescia monastery (late 9th – early 10th Century). The name Oldofredi comes from the noble family from Iseo, but there are no documents that affirm the ownership or use.
The oldest section is the keep (late 11th -early 12th Century) in the southern wing and no longer visible from the outside. It is square in shape with the sides measuring about 10 m and cut off about 12 m from the base, with thick stone walls. It was probably part of the castrum burned by Frederick Barbarossa in 1161 and, if so, was spared from the devastation, as it was already described in 17th Century sources.
A new castle with a rectangular shape was built on the site of the castrum between the 13th and 14th Century, consisting of rectilinear curtain walls defended by square mural towers on the corners; these towers had one side open to the inside and a scarp base. It was surrounded by a deep ditch dug in the rock, which is partly filled today. It was entered from the north and south by two pointed arch doors and, in the keystones, there was the coat of arms of the powerful family of the Scaliger from Verona, who entertained political relations with Oldofredi in the early 14th Century. Both doors were preceded by large protruding avant-corps that allowed carriages and pedestrians to enter; they were closed by wooden doors and a portcullis (vertically-closing gate) and equipped with drawbridges. The first was protected by a tower, completely missing today, which overlooked the avant-corps, and the second by the keep, which it skirted on its side.
The fortress had the dual objective of strategic stronghold to defend the territory and a military control apparatus for the country. Although its date coincides with the short ruling of the family of the Scaliger in the Brescia region, and their coat of arms is present, it is not possible to determine whether the building was actually one of their fortifier interventions, as it has not yet been determined if the doors are coeval with the rest of structure or whether they are the result of a restructuring in the Scaliger era of a previous complex.
Under Venetian rule, the castle lost its military importance and it became the property of Celeri until 1585, when it was donated to the Capuchin Franciscan friars. It subsequently underwent several different modifications: the irregular triangular ravelin, built beyond the southern moat in the 15th Century to defend against external access to the castle, became the friars vegetable garden; the towers were severed; the church of San Marco (St. Mark) was built and consecrated in 1629, with a single nave, barrel vaulted with side groins and a façade decorated with false architectural elements.
The two story section was added outside the north wall and the buildings along the three sides of the courtyard were built between the 17th and 18th Century. The southern section has a portico and a loggia consisting of arches supported by rectangular shaped brick pillars. On the ground floor there is a 17th Century fresco depicting an exchange of gifts between a friar and a number of individuals in oriental robes; the remains of a Crucifixion can be seen in the loggia. 18th Century frescoes can be found along the staircase leading to the upper floors (Our Lady of Mercy, St. Fidelis of Sigmaringen), on the first floor (Ecce homo, St. Anthony of Padua) and on the courtyard entrance hall (Annunciation).
With the Napoleonic suppressions, the friars abandoned the convent in 1797 and the complex became private property, it was eventually converted into apartments. It was purchased by the Iseo Town Council in the 1960s and restored. Today it partly maintains its residential function but is also the seat of the town library, the War Museum, some cultural associations and, in the former church of San Marco (St. Mark), the civic hall.