Masjid, wherein here termed as Mosque, is the worship place for Muslims, now the origin of Islam (religion of the Muslims), is Saudi Arabia. Saudi Arabia is a hot country, so in order to keep out the heat and the Masjid cool on inside, the walls and roofs are made thick. And the dome, interestingly makes the room more cooler.
Now this design has spread with the spread of Islam from Saudi to various parts of the world.
Now speaking of the design of the Masjid's, i find it quiet amusing rather than bulky. The 'bulky' design is a combination of a unique architectural design as well as engineering that was developed around 1450 years ago. The engineering part lies in 1.Thermal insulation 2. The reduction of vertical support columns in the central part of the building, and 3. Sound amplification and echo inside the building. The increased height and the dome plays a great role in sound amplification as well as echo generation.
So its really a impressive and amazing design.