It begins with some sparkling action — a motorbike/fisticuffs getaway in Bangkok — and lopes into a jaunty railroading escape in rural Thailand.

There are self-aware jokes ridiculing the silliness of the very idea of a magical “fountain” that bestows health, eternal youth and the promise of wealth.

There’s even a hint of self-awareness as the action adventure rips off Indiana Jones, “Da Vinci Code” and “Tomb Raider” and the like.

You think “We’re in ‘National Treasure’ territory. Maybe all this nonsense will make sense. Somehow.”

But as the dialogue never-quite-overcomes its creakiness and the story veers towards “The Mummy” and the laughs and suspense never really show up, one can feel the wind going right out of the cast’s performances. They get that “At least the check cleared” look in their eyes.

Guy Ritchie’s “Fountain of Youth” makes you feel embarassed for the players, because they can’t hide the sheepishness that sets in having to mouth bad lines in a ludicrous story that just drags on and on with a dogged resignation that “We’ve got to get through that ‘Lost Ark’ finale, kids. Make the best of it.”

John Krasinski plays Luke, an underhanded antiquarian who isn’t above stealing famous paintings to get him where he’s going.

Natalie Portman plays his museum currator sister Charlotte, who loses her British National Gallery job when Luke ducks in to catch up, and oh, steal a Rembrandt.

There’s this rich oligarch (Domhnall Gleason) who is dying and who is determined to find the mythic “fountain of youth” to save himself. And our siblings, the children of a famous archeologist, are compelled to humor him because he’s got gobs of money and their late archaeologist/dad taught them that myths shared across many cultures must have a little truth to them.

So they’ll “chase this pot of golf” because “life is about the adventure,” and “the journey’s more important than the” destination.

Love that John Krasinksi. But he can’t hide how let-down he must have felt as he recited these hokey lines, and others like them.

The quest that Charlotte is roped into involves clues hidden in paintings by the Renaissance masters, a “Da Vinci Code” dash through a puzzle that will reveal a location for the fountain that isn’t in Florida. They hope.

They will raise a long-sunken ocean liner (Because why dive to it to retrieve an artifact?), venture from London to Vienna and beyond, doing whatever it takes because “Moneybags” has deep pockets and no time for following the rules.

Every time Charlotte says “We’re NOT grave-robbers,” we and Portman and anybody with a lick of sense thinks “Yes, you are.”

They are pursued by a sexy-flirty-but-deadly representative (Eiza González of “The Ministry of Ungentlemanly Warfare”) of people who want any such mythic fountain kept a secret (Big Pharma?) and an Interpol agent (Arian Moayed) determined to bring the art thief Luke to justice.

The violence is mostly comical until it abruptly shifts to body-count bloody in the third act. The “fun” is long gone by then, anyway.

Krasinski and González manage some light mid-brawl banter that hints at “chemistry” that the script doesn’t really provide.

Portman soldiers through it, with Gleason at his least inspired and Ritchie helming his uncoolest clunker since his divorce from Madonna.

Most of the players give away how badly they figure this is turning out in the performances, especially in a one-scene turn by the last “big name” in the cast.

If Portman, Krasinski, Gleason and even Stanley Tucci seem embarrassed, we can’t help but feel embarrassed for them.

Rating: PG-13, violence, lots of bloodshed

Cast: John Krasinksi, Natalie Portman, Eiza González, Domhnall Gleason, Carmen Ajogo, Laz Alonzo and Stanley Tucci.

Credits: Directed by Guy Ritchie, scripted by James Vanderbilt. An Apple TV+ release.

Running time: 2:05