3.Is it possible that someday we may seek to add further to our comfort and security by building our houses undergroundi new,manmade caves? add to:increase e.g.The many newly-built first-class hotels have added greatly to the beauty of the city. 3. Is it possible that someday we may seek to add further to our comfort and security by building our houses underground — in new, manmade caves? add to: increase e.g. The many newly-built first-class hotels have added greatly to the beauty of the city