There are many of these loops in Amsterdam, one at each end point except those on the lines to IJburg and Amstelveen which are operated by bi-directional trams. Also Rotterdam and The Hague have many loops as I believe all trams in Rotterdam are unidirectional and most in The Hague are.
Regarding Rotterdam you're right, they only have unidirectional trams. In The Hague however more and more trams have become bidirectional: all RegioCitadis trams at RandstadRail (between The Hague and Zoetermeer) are, as well as the relatively new Siemens Avenio trams. There still are routes which are operated with the old GTL stock which is unidirectional however, which obviously have loops at the end.
The remarkable thing in The Hague is however that they also have quite a few loops at routes only served by bidirectional trams:
- Route 11 has a loop both in Scheveningen Haven and at Den Haag Hollands Spoor station, in both cases there is no space for tailtracks
- Route 2 has a loop in Kraayenstein (but a tailtrack in Leidschendam)
- Route 9 also has a loop at both Vrederust and Scheveningen Noorderstrand, for the obvious reason it shares the loop in Scheveningen with route 1 (ran with unidirectional trams)
- Route 34 (peak-hour service) has a loop at its The Hague terminus, although the remainder of the tram lines it runs on was rebuilt to bidirectional operation.
- The brand new terminus at Delft University (not yet in service) has a loop, although route 19 which will eventually serve it runs with bidirectional trams (and cannot do otherwise, as its other terminus doesn't have a loop)
Several of the mentioned routes by the way have island platforms, so despite having a loop cannot be served with unidirectional trams.