In perhaps the biggest neighborhood block party the city has ever seen, spectators from across the Bay Area headed to downtown San Francisco on Saturday to celebrate the grand opening of the Salesforce Transit Center and its 5.4 acre rooftop park.

The long-awaited regional transit hub, touted as “the Grand Central Station of the west,” has been in the works for two decades and under construction for eight years, evolving from a three-block construction site to a sprawling urban oasis. Although the street-level terminal has been servicing the 5, 7, 14 and 38 Muni lines since June, last weekend's event celebrated the opening of the rest of the building and rooftop park to the public.

The block party attracted such large crowds that eventually officials had to limit the number of people coming in, citing capacity issues.

Throughout the afternoon, transit enthusiasts lined up outside the Mission Street entrance for a free tote bag before gathering in the Grand Hall to take photos and watch performances by local music and dance groups.

Cameras were abundant as visitors entered the Grand Hall, which features a bright and expansive atrium, glass skylights and a scrolling LED art installation by New York-based artist Jenny Holzer. A towering digital display along Fremont Street listed bus departures and locations, while escalators shuttled travelers to and from the building's bustling upper levels.

On the third-level bus deck, transit agencies from across the Bay Area took part in the Historic and Contemporary Bus Expo, showcasing a wide variety of vintage and modern buses, including a new double-decker AC Transit bus set to hit the roads in the near future.

The bus deck will be the terminus for several regional transit agencies, including AC Transit, Greyhound, Amtrak, WestCAT Lynx, as welll as Muni's 25 Treasure Island line.

Also brand new to East Bay commuters is the bus ramp, a dedicated accessway that connects buses directly to the freeway. Attendees on Saturday had the chance to take a “once in a lifetime” photo on the empty, Bay Bridge-inspired ramp before it opened for service the following morning.

Atop the transit center's open-air roof, visitors got a first look at Salesforce Park’s 5.4 acres of walking trails, grassy lawns and botanical gardens. Live music and pop-up food vendors circled the main plaza, where an abundance of tables and chairs provided a place to sit and admire the view.

From its high-rise vantage point, the park offers a glimpse into surrounding office buildings, including Salesforce Tower and 181 Fremont (home to Facebook’s San Francisco office), both of which have direct access to the rooftop's public space.

An outdoor amphitheater faces the west end of the park, surrounded by a flat lawn that accommodates up to 800 people. The stage hosted its first performers on Saturday with a DJ set, free yoga and dance classes, a kids movement class and a Shakespeare Scene Sampler performed by the African American Shakespeare Company.

Aiming to entice visitors of all ages, the park includes a number of family-friendly amenities, such as a children’s play area, an arts and crafts station, and mobile carts full of books and board games.

And although it wasn’t in action during the grand opening festivities, the northern edge of the park features an interactive water fountain activated by passing buses below, which adults and children alike are invited to play in (should San Francisco weather ever warm up enough).

Open to the public daily from 6 a.m.-8 p.m., the park will host a full schedule of free events in the summer and fall, from fitness classes to writing workshops to public music and theater performances. A complete list of events can be found at the Salesforce Transit Center website.

If the park's many events aren't enough to draw a crowd, the transit center is also a canvas for public art. Colorful flowered patterns grace the Grand Hall floor as part of Julie Chang’s "Secret Garden," and a wall of murals spans the southern side of the building along the Natoma Pedestrian Way.

A project by nonprofit organization ArtSpan, the murals feature paintings by 38 local artists, covering 10,000 square feet along Natoma between First and Second streets. They will remain on display until retail tenants start moving in.

As for soon-to-debut amenities, the Salesforce-sponsored gondola (originally set for June debut) will start operating in September. And retailers are expected to begin filling the center's 100,000 square feet of retail space in 2019.

Saturday's festivities celebrated the completion the $2.26 billion first phase of the larger project. The next phase is a 10-year project to build an underground train platform that will eventually serve Caltrain and the California High-Speed Rail.

For updates from the transit center's first week of full operation, follow @TransitCenterSF on Twitter.