In terms of quality and originality, Bhutanese architecture is without doubt one of the best expressions of the Thunder Dragon Kingdom's unique character. Almost completely isolated for many centuries by its complex geography, Bhutan has indeed seen very few changes in its architectural system since the earliest times. The architecture of Bhutan is one of the Kingdom’s most visible distinctive features. The massive Dzongs (fortresses) with their upward sloping walls, the ancient monasteries and the humble farm house stand out as an important part of the country’s landscape. Each valley in Bhutan retains its own architectural character in terms of the type of building material used, ranging from mud to stone, and the special ambience of its most famous monasteries and Dzongs.