Combined bike and train.
Bike to train station, get on train, change trains, get off train, bike to office. (5km ridden)
Heading home is a bit different, owing to restricted bike access to trains during rush hour. Bike to train station, get on train, get off train just before central station, bike home. (12km ridden)
On the up-side, bikes cost nothing extra. On the down-side, you cannot take them onto trains travelling in the peak direction during peak periods.