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Morning light floods an indoor privately owned public open space at 222 Second St. in San Francisco.

A sign directs guests to an indoor, privately owned public open space at 222 Second St. in San Francisco.

Allegra Thomas takes a break from her nearby office to enjoy the quiet and tranquility of the rooftop terrace at 150 California St., San Francisco, in 2015.

The 11th floor terrace of One Kearny in San Francisco provides a unique glimpse of the regal mansard roof of the 1906 landmark to which it is attached.

Office workers grab lunch from a cantina beneath an indoor privately owned public open space at 350 Mission St. in San Francisco.

Even before the pandemic, some of the coolest public spaces in downtown San Francisco were easy to miss — perched on tall buildings or tucked inside towers, off the map unless you were in the know.

One two-tiered interior space features Frank Stella artwork on red teak walls. Another has a snug terrace nestled against the structure’s ornate stone cornice — 11 floors above Market Street.

Then came COVID-19. Now, even though workers are returning to the city’s downtown core, some of the best public spaces remain off limits.

We’re still living in harrowing times, no question. But at some point before too long, the city will need to give an official prod to building owners who otherwise might try to make private amenities out of community benefits that they are required to provide.

The nooks and aeries in question are required by the city’s Downtown Plan from 1985, which made room for the Financial District to expand south of Market Street while keeping heights low in neighborhoods like Chinatown and North Beach. The legal nexus was simple: If you add a large daytime population to an area where there are no parks, then the new buildings should provide outlets for workers and visitors to have spaces where they can kick back or let off steam.

The program even has its own wonky acronym: POPOS, for privately owned public open spaces.

Since then, at least three dozen have been created, and most are conventional plazas. In some cases, though, developers chose to create upper-floor terraces or atrium-like gathering spaces — including a few with glass walls along the sidewalk that could pivot open or slide back, erasing the line between indoors and out.

When COVID-19 descended in 2020, those spaces closed down like everything else. Workers weren’t allowed into buildings. Downtown’s landscape went from vibrant to vacant.

Artwork hangs above an indoor privately owned public open space at 181 Fremont St. in San Francisco.

The pandemic continues, as each new variant makes all too clear. But offices are reopening. Workers are trickling back. Financial District sidewalks and the blocks around Salesforce Tower show welcome signs of life.

Indoor spaces now mostly have reopened, some much earlier than others. The expansive teak-clad room facing Howard Street in the LinkedIn tower, with its Frank Stella artwork and plentiful seating, has beckoned as an oasis for months; the glassed-in “greenhouse” at 101 Second St., the most popular of these spaces in pre-pandemic times, only made it possible last week to enter the space if you weren’t a tenant with a key card to swipe.

Most of our supposedly “public” rooftops, though, remain closed off.

There’s one big exception: 150 California St., where you sign in with the security guard and then can enjoy a lavender-landscaped sixth-floor terrace. Otherwise, good luck reaching such seductive peaks as the summits of One Kearny and 343 Sansome St.

The latter is a startling high point, literally, of the traditional Financial District — an easily accessible elevator ride leads to a variegated landscape that feels wholly detached from the commotion below, with views that jumble together nearby buildings and the natural bay. The former is a snug retreat that feels almost balcony-like, albeit a balcony that allows you a telescopic perspective on Twin Peaks to the west or Third Street to the south, depending on your mood.

While 343 Sansome’s rooftop has been a lunchtime favorite since it opened in the early 1990s, the owners now are renovating the space as part of a larger building renovation (let’s hope they don’t get rid of all the trees, a relaxing counterpoint to the hard-edged cityscape). I’m told it should reopen by the end of the year; until then, to quote signs at each building entrance, “Roof deck closed due to construction. We apologize for the inconvenience.”

An indoor privately owned public open space is seen at 55 Second St. in San Francisco.

At One Kearny, which never has been particularly welcoming, the posted explanation is much more vague.

“Due to COVID-19 virus concerns, the 11th floor rooftop terrace will be closed,” it shrugs. “We anticipate the closure to continue until the threat of the virus spread has subsided.”

How’s that for open-ended?

At another building with a public rooftop, the Hampton Inn at 942 Mission St., a clerk at the front desk will inform you politely that the 15th floor terrace is closed to the public for now — except that the tower’s automatic sliding door that leads to the front desk rarely opens up to let outsiders in.

The sixth-floor rooftop of 543 Howard, which offers a great view of the tower-ringed transit center, keeps its lobby locked tight.

This is what’s dicey about every “public” space that requires entering a private building: The ultimate control is in private hands. Outdoor plazas are open to all, perceptually, no matter what codes of conduct the owner might try to apply. But if you can’t get in, or you don’t know it’s there, then even the most sumptuous semi-public nook might as well not even exist.

This has always been the case, which is why the Board of Supervisors in 2012 required metal plaques with larger lettering than what existed before. It will be even more of a challenge in coming months, as we navigate a communal future that is murky at best.

Some owners probably hope that the concerns about downtown, from the dangerous persistence of the pandemic to the deterioration of the public realm on some blocks, will provide cover for skirting their obligations.

But the fact remains: These are public spaces. And rooftops are nothing if not naturally ventilated. That’s an essential amenity these days.

The rooftop garden at 343 Sansome Street is seen in 2016 in San Francisco.

The indoor spaces offer a different benefit: controlled comfort in a climate that can shift by the hour, especially with tower-induced winds. The seventh-floor space at 181 Fremont St. that can be entered via footbridge from the rooftop park of Salesforce Transit Center is already humming, especially with the added lure of an outpost of the Outer Sunset’s Andytown Coffee Roasters. The LinkedIn tower’s space usually has a few people inside, even though its coffee bar hasn’t yet reopened.

“It’s a public living room,” Carl Shannon, senior managing director at Tishman Speyer, the developer, said with a shrug. “It’s part of our commitment to the city. We want it to be successful.”

There’s no single prescription for restoring downtown San Francisco’s vitality. One key, though, is to emphasize aspects of the landscape that you can’t find anywhere else. The unique nooks that exist within the Financial District can be part of the appeal — and the sooner that owners accept this, the better off we all will be.

Until then? If you’re downtown and see a plaque signaling a public space behind closed doors, pop in for a look. You might find yourself staying longer than you expected.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron

A thorough map of downtown San Francisco's privately owned public spaces - and tucked-away public art as well - is at https://sfplanning.org/privately-owned-public-open-space-and-public-art.

John King is The San Francisco Chronicle's urban design critic, taking stock of everything from Salesforce Tower to sea level rise and how the pandemic is redefining public space. A two-time Pulitzer Prize finalist and author of two books on San Francisco architecture, King joined The Chronicle in 1992 and covered City Hall before creating his current post. He is an honorary member of the American Society of Landscape Architects.