Ah, I love those big chunks of clear crystal. Czech, German or Scandinavian is all I can say with certainty about it. Sadly I've never seen this one before (or I would have bought it).
For reference it would help if you could indicate the dimensions.
I can however speculate a bit further.
The base looks polished flat, is that right? Sklo Union pressed crystal usually has a bird bath base. Perhaps it's Podebrady, they use flat bases, but they usually make cut crystal, this one looks more pressed?
It could certainly be German from the 70s. I assume you already looked very carefully for an etchmark on the base or closely above it. This is the sort of clear piece that could be made by Peill & Putzler (but it would be usually marked with a double P etched on it), or Nachtmann (usually unmarked). There are a few smaller companies that could have produced it, but research on German glass is still quite sketchy and for the pioneers, so many pieces remain unattributed.
As for Scandinavian glass, it's not blue enough for Strombergshyttan. It could be from another Swedish company like Skruf. Scandinavian glass is often signed, but not all of them are.
Well, hope this helps in exploring more search directions.
Astrid