With so much to see and do in The Golden City, you'd be forgiven for missing some of the hidden gems in San Francisco. Tons of treasures on less-beaten paths, with quirkier features, and many secret green spaces are tucked behind big hills and billionaires' houses. Leave the big stuff for the tourists (you've already crossed it all off your bucket list, right?!), and explore these 12 hidden gems in San Francisco.

1. Privately-Owned Public Open Spaces

This is actually a combination of 68 (!) spots throughout downtown San Francisco, affectionately called POPOS. It's a mix of small urban parks, gardens, sun terraces, greenhouses, plazas, and patches of green perfect for a quick midday sunbathing session, an outdoor lunch, or an impromptu meeting. This one is located at 555 Mission. Here is an excellent guide to them all.

2. Ina Coolbrith Park

Reaching the top of this mini park (beware: you pretty much have to go up a hill, no matter the direction you're coming from) will give you some of the best views of Coit Tower, the Bay Bridge, and Alcatraz. Named after the first American poet laureate who lived just a block from here (pre-1906 earthquake), this is the place to bring your date for a lovely sunset moment.

3. Mount Sutro

The location itself is not so hidden (you can spot Sutro Tower looming over the city nearly everywhere), but few know that this is a great place for a leisurely uphill hike that takes you through a dense eucalyptus forest. Come on a foggy day and you may feel like you're walking on the clouds.

4. Wave Organ

Completed in 1986, this Marina District structure is certainly not the prettiest sight, but that's not the point: This is meant to stimulate your ears, not your eyes. Sound is created as the Bay waves move in and out of organ pipes made of PVC and concrete. Plan to come at high tide and prepare to be hypnotized by one of the best San Francisco hidden gems.

5. Lovers' Lane in the Presidio

Just outside of "Billionaire's Row" is this windy art installment disguised as a natural wonder. Bring your lover (of course) and follow the snaking logs (or take the parallel concrete path) for a short little hike and amazing Instagram opportunities.

6. Golden Gate Heights (16th Avenue) Mosaic Stairway and Grandview Park

There are lots of cool stairways sprinkled throughout the city, but this one designed by local artists may be the most stunning. Keep going up and do the loop up to the top of Grandview Park, another hidden gem that offers some incredible 360-degree views.

7. Seward Street Slides

Grab a piece of cardboard and be transported back to childhood at this hidden Castro spot. A slide can truly be one of the greatest simple pleasures in life, after all. Oh, and bring a friend so you can race!

8. Camera Obscura

There's so much beauty at Lands End, that most people miss this cool little camera house. Inside, you'll catch a 360-degree image of the Seal Rock area right outside. The whole device depends on the sunlight, which means you want to try to make it here on a fogless day.

9. Tank Hill

This small hilltop park is often overshadowed by its Twin Peaks neighbor, but it guarantees just as spectacular views of the whole city, the Golden Gate, and the Bay. Grab a spot on the perfectly located bench and take it all in.

10. Balmy Street Murals

While most people will go straight to Clarion Alley, this other colorful Mission passageway, just off 24th Street, offers the most concentrated collection of murals in the city. It's an incredibly vibrant sight to take in — every bit of the wall is covered by gorgeous artwork that speaks to local issues, human rights, and gentrification.

11. Strawberry Hill in Golden Gate Park

Can't get enough of the hills (or the views)? Us either. This gem inside Golden Gate Park sits in the middle of Stow Lake and can be accessed by one of two adorable bridges. You can take a few different trails (there are also steps) that wind around the hill. The summit offers some views of the Golden Gate Bridge and downtown.

12. Ingleside Terraces Sundial

Standing 28 feet tall in the heart of the Ingleside Terraces neighborhood is this huge sundial sculpture (and, yes, it works!). It was built back in 1913, and it proves that this side of the city does indeed see the sun! Discover more about one of the best hidden gems in Northern California on the North American Sundial Society website.

Have you been to any of these hidden gems in San Francisco? All of them? What else did we miss? Let us know in the comments below. And while you're traveling through this stunning city, find a cool place to stay on Expedia.com.