Complex sentence: Most of the walls of the castle are painted black, it is a strong structure, built to withstand warfare while at the same time it is majestic and solemn, reminiscent of the Momoyama style.
Split into simpler sentences: Most of the walls of the castle are painted black. It is a strong structure, built to withstand warfare, yet at the same time it is majestic and solemn, reminiscent of the Momoyama style.