Lullabies for Time Tots

Lullabies for Time Tots was written by the Benncuiq III. (PROSE: When It Was Fun) It told the story of the Death Zone and the Tomb of Rassilon. (TV: The Five Doctors) It went,
 * Who unto Rassilon's Tower would go
 * Must choose - Above, Between, Below
 * Who unto Rassilon's Tower would go
 * Must fight with those he used to know
 * Who unto Rassilon's Tower would dare
 * Must dance across the deadly square
 * If Rassilon's Tower you step in
 * Then you must choose - to lose or win

At some point it came into River Song's possession while she was researching the Fifth Doctor. (PROSE: When It Was Fun)