An absolute classic. I read this several times as a child so I was happy to come across this audiobook. The gist of the story is that this mysterious spacecraft that contains a whole miniature world comes hurlting into the solar system. A small band of explorers enter it and try to figure out its mysteries -- much to no avail. A classic Arthur C. Clarke story told with a scientists dispassionate eye.
http://www.amazon.com/exec/obidos/tg/detail/-/0553287893/qid=1123164428/sr=8-1/ref=pd_bbs_1/002-3080515-8227250?v=glance&s=books&n=507846
