Houston’s Buffalo Bayou Park, a sprawling urban greenway that wraps around the city’s beloved “Mother Bayou,” officially reopened last October with considerable fanfare (and a fireworks show, natch) following a multi-year, $58 million renovation and revitalization project.

Spanning 2.3 miles from Shepherd to Sabine streets along Buffalo Bayou just northwest of Houston’s skyscraper-laden downtown, the 160-acre green space has undergone quite the makeover, remerging with a pair of fancy new visitors centers, a 2-acre terraced dog park, a quartet of bayou-traversing footbridges, a massive skate park, kayak rentals, al fresco performance and event spaces, a wealth of public art and statuary, restored woodlands and a stunning new wetland nature park complete with hiking and biking trails. Phew.

And because this is Houston, a city where the summertime heat will essentially destroy you, the park has gained additional shade structures.

While all of these new and improved features make for one brilliantly rejuvenated urban green space, Buffalo Bayou Park’s newest and most extraordinary attraction isn’t exactly new — even though a majority of Houstonites have never set foot in it, let alone knew it even existed.

This new crowd-drawing feature, which opened to the public earlier this month, doesn’t take advantage of the park’s outdoor recreation-friendly, on-the-bayou locale; there’s no sweeping downtown views, picnic pavilions or bike rentals here. Hell, it’s pretty hard to find — and that’s largely because the unlikely crown jewel of the new Buffalo Bayou Park is located underground.

Location of the Buffalo Bayou Park Cistern The Buffalo Bayou Park Cistern is located just off of Sabine Street just west of downtown Houston. (Image: Google Maps)

Dubbed the Buffalo Bayou Park Cistern in homage to the ancient Roman cisterns buried deep beneath the streets of Istanbul, this decommissioned subterranean reservoir-turned-star park attraction was (re)discovered somewhat by happy accident.

During the beginning stages of the park’s overhaul, city officials made it clear that they planned to demolish the defunct old reservoir hidden beneath the park's under-development great lawn. Built in 1926 to store Houston's drinking water supply and supply water for municipal fire suppression, the positively massive — 87,500-square-feet! — reservoir was in active use all the way through 2007, several years after a non-repairable leak was detected.

You could say that the Buffalo Bayou Partnership, a nonprofit dedicated to the revitalization of the bayou through park-building projects and conservation-minded endeavors, wasn’t on the same page as the city regarding the ultimate fate of the architecturally significant reservoir. Sporting 221 slender concrete columns that support the 15 million-gallon holding tank’s 25-foot-tall ceilings, the reservoir takes on the appearance of a mysterious sunken cathedral — the kind of place the Teenage Mutant Ninja Turtles might worship if they were practicing Catholics, not crime-fighting testudines.

The partnership believed the the reservoir, with its evocative appearance and historic appeal, needed to be saved and repurposed

And so, a deal was worked out that transferred development and maintenance responsibilities of this curious hidden jewel from the City of Houston to Buffalo Bayou Partnership. Subsequent grants secured from the Brown Foundation totaling $1.5 million enabled the partnership to bring the space up to code (guard rails, lighting, emergency exists and all that good stuff) and, in turn, allow for tours and art installations.)

The city’s first underground drinking water reservoir — a “dark, accidental beauty” per the Houston Chronicle — was going public.

Since going public on May 13, the Buffalo Bayou Park Cistern has welcomed hundreds of curious Houstonites and out-of-towners on docent-led tours. Site-specific art programming will be introduced in the coming months.

To be clear, the rehabbed reservoir isn’t a free-for-all. Advance reservation must be made to embark a 30-minute tour of the space; the tours cost $2 per person except for on Thursdays when access is gratis. Kids under the age of 9 and a variety of items — chewing gum, dogs, strollers, etc. — are verboten.

What’s more, there’s this compulsory heads-up:

The Buffalo Bayou Park Cistern is a dim space with no windows. The environment may be challenging for some. If you experience any difficulties, please proceed directly to the nearest exit.

For claustrophobics or those who may become panicky within the confines of a 90-year-old concrete echo chamber as large as one-and-a-half football fields, New York-based artist Dan Lipski has devised a clever way to experience the Cistern without going underground in the form of “Down Periscope.”

Commissioned by the Houston Arts Alliance in partnership with the City of Houston, “Down Periscope” is a 7-foot-tall periscope that lets park-goers peer directly down into the murky depths of the reservoir from a shaded kiosk installed on the lawn above. What’s more, users can step up to the periscope online although, like being there in the flesh, there’s a queue to take a 5-minute-long-max peek. (I waited just 90 seconds for my turn ... not too shabby).

While the Buffalo Bayou Park Cistern is certainly the first underground reservoir to be converted into a public arts space-cum-extension of an aboveground park in North America that I know of, other cities are increasingly looking down as part of a larger movement that taps into the potential of hidden and neglected urban spaces. New York City’s proposed Lowline is envisioned as verdant underground park that harnesses innovative light collection technology to naturally illuminate a reclaimed area hidden beneath the Lower East Side of Manhattan. In Washington, D.C., the now-open Dupont Underground has repurposed an abandoned trolley station and transformed it into a bustling subterranean arts hub.

As summer kicks off in Houston, the timing of the Buffalo Bayou Park Cistern couldn’t be more perfect. After all, what a better place to beat the oppressive heat than within a sprawling underground water tank?

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.