KW and BC strolled inside Exploratorium in San Francisco on the Fourth of July to take in some of the cool exhibits, which include the "Cafe Wall Illusion," "All Eyes On Me," and "Fog Bridge."

One photo captures Kanye seated across from Bianca at a mirror exhibit.

We're told the famous lovebirds were totally engaged with each other as they walked around like ordinary citizens eyeballing the various displays. Other people, of course, recognized the two, but stayed away -- not wanting to intrude in their space.

Our sources say Bianca was her regular sexy self, wearing white see-through leggings with a blue strapless top and heels. For Bianca, the only shocker was that her body was almost completely covered -- a rarity for her.

Kanye, on the other hand, took the top prize for his outfit, donning something resembling a white, baggy spacesuit with matching sneakers. Going to the moon, Ye?

TMZ obtained several photos of the pair enjoying their little outing ... In one image, the two were seen holding hands as they maneuvered through the museum.

Another snap shows Bianca on a red phone listening to scientific facts near the entrance of the building.