Schwarzenegger visited the Valley of the Fallen near Madrid while in the Spanish capital to promote martial arts extravaganza Arnold Classic Europe.
He spent a little over an hour at the site and declared himself "pleasantly surprised" at the scale of the massive complex, according to the website of the association that oversees the monument.
But the actor's decision to visit the site received a mixed response from the Spanish public.
The Valley of the Fallen was conceived by Spain's right-wing dictator Francisco Franco who ruled Spain from the end of the country's civil war in 1939 to his death in 1975.
It also the final resting place of the dictator.
The huge crucifix and the Catholic church on the site were partly built by convicts, including political prisoners, and the site remains controversial.
"No wonder he visited the Valley of the Fallen, his father was a Nazi," wrote Twitter user Paco Lobo.
Twitter user @RuthMts wrote: "Schwarzenegger in the Valley of the Fallen with the fascist allies of his father."
The vast majority of reactions to the one-time bodybuilder's visit were, however, humorous.
"At last Franco can rest in peace," wrote Javier M.P.
Schwarzenegger "must have confused Franco with (actor) Danny DeVito" tweeted Aithor Maiden.
The visit by the ex-Governor of California was "strictly private", stressed Pablo Linares, the head of the Valley of the Fallen association.
That didn't stop Linares taking a few photos of the Terminator as he took in the sights, and then posting them on the association's website.