This review contains so-so spoilers.
This episode feels like a reunion show. It has the return of Jason and several of the Argonauts (from 'Once A Hero'), the Blue Priest (from the TV movie 'Hercules and The Lost Kingdom', Dirce (from 'The King Of Thieves'), Deric the centaur (from the first season's 'As Darkness Falls' and the second season's 'Outcast'), the 40 virgin sisters (from the first season's 'Eye of the Beholder'), and Iphicles (from 'What's In a Name?') ... Not to mention another appearance of fast food salesman Falafel, and a cameo by Salmoneus at the end. Did I miss anybody??
At the start of the episode, I thought it was an average one, with not the most interesting of stories. But as things progressed, and more and more faces from previous episodes turned up, I began to like it more.
The highlight of the story is Jason and Hercules being swallowed up by another of Hera's giant sea serpents, this one called Perfidia. Unlike the first one (seen in 'Hercules and The Lost Kingdom'), this one had a body and legs too (does that still make it a serpent?). Unlike the first serpent, which was done mostly with model work, this one is entirely CGI, and for the most part, very well animated. So Herc and Jason are gobbled up inside (good job these giant serpents never chew their food!), and must find a way out. The sets inside the serpent are a cross between scary and surreal.
This episode, with all of the returning characters (and the final set piece inside the serpent), this episode feels like it was designed to be the season finale, and I don't know why it wasn't used as such – it would have served much better than clip show 'The Cave Of Echoes'.
All-in-all... its starts off as a rather average fare, but turns out to be an exciting, enjoyable one.