Pengkalan Kakap Old Mosque is known as the Stone Mosque (Masjid Bat). The Pengkalan Kakap Mosque is among the few national heritage mosques built near the historical site of the Bujang Valley in Kedah. Located not too far from Merbok.

The mosque had been a popular stopover among the Muslim traders doing business at the Merbok Harbor, especially amongst the Acehnese traders from Sumatera. The mosque was also a favourite stopover by the then Sultan of Kedah, Sultan Abdul Hamid, during his trip to the district.

The double-pitched roof made of clay tile material, features a double-tiered roof style, a twist to the norm Meru pyramidal root. The hip roof expanse covers the square layout of the mosque building that comprises the main prayer hall, overspill area and extended roof to cover the veranda area. The overspill area is marked by a series of Doric-order columns, with one meter (three feet) concrete wall railings. The entrance way is slightly raised with three steps, possibly to prevent flood waters from entering the main prayer hall. The floor of the main prayer hall is also raised for the same purpose. Inside the main prayer hall, six octagonal columns stand across the space and sit on concrete base stumps. Although the perimeter wall is relatively low, the columns give a monumental height effect to the Interior space due to the
elevated tiered roof form. The exposed roof structure allows views of the rafters and the clay tiles from below. An old chandelier hangs above the space leading to the front qibla wall. It is signified by a shallow round niche, possibly the former mihrab, with five steps made of bricks which was possibly part of the minbar structure.