I've been experimenting with writing englyns – these are complex, rigid Welsh poetic forms – not in Welsh, though. This is a small englyn penfyr I made:
nobody sees sky's glimmer, the sun falls,
-nobody feels the summer-
nobody sees air's shimmer.
Sometime back I tried writing one in Spanish, too – probably not as good. And this one is about being angry:
a veces siento enojo de perro,
ira de piedra, un rojo
enfado de hombre cojo
Traditional Welsh poetry is fascinating to me because of its demands for such highly structured forms – almost like Japanese haiku, for example. And, as Georges Perec once pointed out (and probably others), it is constraint that leads to truly innovative artistic expression, and not freedom.
I remember as one of my most productive periods of poetry-writing the time when I was experimenting with highly constrained forms such as the alexandrine sestina, with additional non-traditional constraints on such things as "characters per line" (thus I could produce completely justified poetic lines using monospace type with no additional spaces).