The Luas, Dublin's tramway (not to confuse with the good auld trams that used to run along Dublin metropolitan area) is a pleasant mean of transportation. It is relatively safe too (when it doesn't collide with Dublin Bus). It's a pity one can't take the bike on board though.
But no worries, some cyclists don't let this fact spoil their Luas experience. They just follow the Luas tracks while pedalling.
Needless to say that this is a dangerous behaviour and a careless way to cycle, it's not recommended and there have been a number of occasions where the Luas overran a cyclist (just two examples from the last year can be found here and here).
There are so many roads and cycling tracks, even next to the Luas tracks, that I'm not quite sure what's the benefit of using the tramway.
I took this photo on 29 May 2012 along the Luas red line. Sadly, it's quite common to see cyclists there.