Picked it up a while ago. It's in 2 pieces, with a smaller glass inside a larger base.
The reason I picked it up was because of the pontil mark (it is, right?), figuring that if someone had taken the trouble to blow this by hand, it should be worth the EUR 0.50. I'm still not closer to finding out what it is, though.
Shape is somewhat irregular, at the base it's 11.5 cm at the longest point, 9.5 cm at the widest. The small inner glass is 5 cm diameter at the rim, and 4.5 at the base.
I thought at first it was some sort of candle holder, but the inner glass is too small for the current size of tea lights. Or perhaps it is meant for very small cacti? Anyway, any help is appreciated.