A wind turbine tower (10) with a guide system for guiding an internal installation unit (20) displaced relative to the inside of said tower (10) to a final mounting position inside said tower (10), said tower (10) having a first end (3) and an opposite second end (5), said first end (3) defining an entry opening for receiving said unit (20), said guide system comprising at least two parallel stays (32) for said guiding being mounted to the inside of the wall (8) of said tower (10) and extending from said first end (3) towards said second end (5), and engagement elements (35) mounted externally on said unit (20), said engagement elements (35) being configured for receiving a respective one of said stays (32).