Recent decline in active transport and increase in motorised transport decreases physical activity and increases air pollution. Using games to motivate people to change their behaviour towards active transport can mitigate this. We proposed Tic-Tac-Training, a distributed, collaborative and competitive game for promoting active transport at workplaces. Tic-Tac-Training was developed through a multidisciplinary and iterative user-centred design (UCD) process in four stages: (i) paper prototype, (ii) low-fidelity prototypes, (iii) high-fidelity prototypes, (iv) digital prototype. User testing and playtesting (N=12) yielded a number of improvement suggestions. We also analysed how Tic-Tac-Training supports the eight core drives of gamification (Octalysis), and presented 17 lessons learned in four categories. Findings suggest that UCD can be useful for developing exergame interventions for workplaces. Moreover, the lessons learned can benefit exergame designers. More research is needed to measure the behaviour change effect of Tic-Tac-Training and its applicability to other use cases.