For one Saturday in October, UCSF Mission Bay will look a little less like a medical and research campus and a lot more like a giant hands-on science playground.

The Bay Area Science Festival returns October 17 from 11 a.m. to 4 p.m. with more than 125 exhibits and experiences designed to make science something visitors can touch, test and explore.

Admission is free, and organizers expect about 15,000 people to take part in what they describe as Northern California’s largest free celebration of science.

This is not the kind of science event where families are expected to stand quietly behind a rope and read display cards.

The emphasis is on doing: experiments, demonstrations, games, stage presentations and opportunities to meet scientists and engineers working throughout the Bay Area.

For younger visitors, that can mean discovering that STEM is much broader than a classroom assignment.

For adults, it is a chance to peek into the research ecosystem that surrounds San Francisco but is often hidden inside laboratories and institutions.

The festival brings together universities, museums, cultural institutions, schools, nonprofits, companies, research labs and government organizations.

That mix is part of the appeal because a visitor can move from one scientific field to another without leaving the Mission Bay campus.

Behind-the-scenes lab tours add another layer for people who want to go deeper.

Those tours are free but have very limited capacity and require advance registration, with small groups visiting specialized facilities and meeting people who work in science, technology, engineering, math and health.

Some tours fill quickly, so the main festival is the better bet for anyone deciding to attend at the last minute.

The bigger idea behind the day is to make the Bay Area’s scientific community feel accessible rather than distant.

That matters in a region where research and technology shape so much of the economy and daily life, yet the people doing that work can remain largely invisible outside their own professional circles.

A free public event gives residents a chance to ask questions directly, see demonstrations up close and let children meet people who actually work in STEM careers.

The location also makes the event easy to combine with a day around Mission Bay, whether that means a waterfront walk, lunch nearby or simply exploring a part of San Francisco that continues to change rapidly.

Families should expect a busy campus and plenty of competition for the most popular activities.

Arriving earlier in the day is a sensible move, especially with children who will want time to stop at multiple exhibits.

The best part may be that nobody has to arrive already loving science.

Curiosity is enough, and with more than 125 ways to put that curiosity to work, there should be something capable of turning almost anyone into a scientist for an afternoon.