One should always meditate in a place of serene beauty. The tea house is therefore specially decorated to make it as beautiful as possible. It is also an ideal place for hosting visitors and formal meetings between among peers.
Tea drinking in Japan is special especially because of its blend with architecture. Some tea houses incorporate simple designs while others are simply a work of art.
Since tea drinking is one of the cultural traditions, it has been passed on from generation to generation. There was a lot of design elements in the old tea house architecture. However,tea houses have advanced in proportion to modern technology and modern design.
Despite the advancements, they still manage to capture amazing design features, thus maintaining the magic of the chashitsu. Source