A place unlike any other
The country of Yemen has many non-architectural tragedies to deal with. It is a failed state. There is more or less anarchy going on, civil war, declining oil prices, a failed popular movement for more democracy and clean government, the operations of a terrorist network and U.S. drone strikes.
Yet it has an incredible rich and fascinating history, a good chunk of which is reflected in its stunning architectural heritage, one that is recognized by UNESCO. But failed states can’t do much to protect that heritage even though heritage is the one thing that might provide an alternative to oil revenues. Of course, heritage tourism is a very tricky and delicate thing: it can ruin places (ex: Angor Wat) or keep them alive while retaining vitality (ex: Dubrovnik). All depends on the management, something in short supply anywhere.
Here are some photos of some of the UNESCO world heritage sites in Yemen. By the way, there are many great books about Yemen architecture. This is the one I have, and it is a gem.