Dah's Caffe is marked by an architectural and engineering oddity: a giant circular air vent rising up from the Sennichimae Subway Line onto the street. On first glance its purpose, and ugliness, are obfuscated by a mosaic of amber tiles. The vent makes its presence felt in the cafe; one wall curves around it to accommodate the structure. But, happily the only aroma in the air at Dah's is the pungent smell of coffee.