The original Blenduk looked nothing like the building that stands today. When Dutch colonists established the congregation in 1753, they built in the joglo style, the traditional Javanese form with a steeply pitched pyramidal roof supported by central pillars. It was a Protestant church, but Catholics worshipped here too, since Semarang had no Catholic church of its own until St. Joseph's was built in the Gedangan neighborhood. The joglo structure served for thirty-four years before it was rebuilt in 1787. But the transformation that created the Blenduk people recognize today came in 1894, when architects H.P.A. de Wilde and W. Westmas spearheaded a renovation that added the copper dome and flanking towers. The church shifted from Javanese vernacular to something far more European in its ambitions, yet it never lost its local nickname.

Blenduk sits in a small courtyard between former colonial office buildings, the Jiwasraya building across the street to the south and the Kerta Niaga offices to the west. The church itself is octagonal, built on a stone foundation with single-layer brick walls. Its dome rides on thirty-two steel beams, eight large and twenty-four small, and is clad in copper that has weathered to a patina visible blocks away. Twin towers flank the main entrance, square at their bases and gradually rounding as they rise to their own smaller domes. Roman-style porticoes with saddle-shaped roofs extend from the eastern, southern, and western faces, while a cornice of horizontal lines traces the building's perimeter. The south-facing entrance features wood-panel double doors, and the windows are etched and stained glass, filtering equatorial light into the interior.

Step inside and the cultural layering becomes tangible. Wooden pews have rattan seats, a material as Javanese as the teak platform beneath the octagonal pulpit. The floor is covered in black, yellow, and white tiles arranged in geometric patterns. Against this tropical interior sits a Baroque pipe organ from the 1700s, now nonfunctional but still present, its pipes silent witnesses to the church's Dutch colonial origins. In the northern corner, a spiral staircase leads to the second floor, its metalwork etched with the name of its manufacturer: Pletterij den Haag, the rolling mill in The Hague. It is a small detail, easily missed, but it traces a direct line from this equatorial city to a factory floor in the Netherlands, a reminder of the colonial infrastructure that built this place and the distances it spanned.

Blenduk has survived more than most buildings are asked to endure. It outlasted the Dutch colonial era, the Japanese occupation, and the turbulence of Indonesian independence. Another series of renovations began in the early 2000s, careful work to preserve what time and the tropical climate had worn. In 2003, the congregation celebrated the church's 250th anniversary. As of 2004, roughly 200 families belonged to the congregation, holding regular Sunday services in a building that doubles as one of Semarang's most visited tourist attractions. In February 2009, the Central Java branch of the Architects' Society of Indonesia awarded Blenduk the prize for Best Maintained Old Place of Worship, an acknowledgment that preservation requires as much devotion as the services held within.

Semarang's Kota Lama, the old town district, is a neighborhood of Dutch colonial architecture slowly being restored and reimagined. Blenduk anchors this quarter. Its copper dome is a fixed point among the warehouses, banks, and trading offices that once served the Dutch East Indies' commerce. The church does not stand alone in its significance, but it stands longest. Other colonial buildings in Kota Lama have been repurposed or left to decay, but Blenduk continues to serve its original function, a Protestant congregation worshipping in the same space where their predecessors gathered in 1753. The Javanese word mblenduk may just mean dome, but in Semarang, it has come to mean persistence.