np

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The best Therion album period.

I'd go with Secret of the Runes. Of course, a lot of people are inclined to write off everything after Lepaca Kliffoth as commercial crap, as if it's no different from sparkly symphonic poppish metal like Epica. However, Secret of the Runes, along with other Therion albums from that era, has a mystery and grandeur about it which elevates them above most other symphonic metal acts.