Complex sentence: In 1937 "Conquerors of the Underground" came out, a finely written novel with a spy thriller element to it and full of technical trivia, which became popular with young, technically minded Soviet readership.
Split into simpler sentences: In 1937 "Conquerors of the Underground" came out. This finely written novel rich with technical trivia and with a spy thriller element to it became popular with young, technically minded Soviet readership.