TAMPA — Bob Buckhorn has worked for nearly 3½ years to put his stamp on Tampa's urban core but never like this.

On Tuesday, the Tampa mayor unveiled an ambitious plan to transform a large but all-but-forgotten park on the edge of downtown into a destination.

Estimated cost: more than $20 million.

"This is a once-in-a-lifetime opportunity," Buckhorn said during a news conference at Julian B. Lane Riverfront Park, 23 acres on the west bank of the Hillsborough River across from the David A. Straz Jr. Center for the Performing Arts. "It's not inexpensive, but I think it is worth doing."

Along with the price tag — a figure that would have buckled the knees of City Hall two years ago — a couple of other things set this initiative apart.

Buckhorn has engineered or supported other big redevelopments: a boutique hotel in the vacant federal courthouse, a new park and restaurant at the fenced-off site of the old city water works, a 36-story apartment tower next to the Straz Center.

Each of those properties, however, was also on the radar of previous mayors, even if their plans didn't pan out.

Riverfront Park is different. Under his predecessor, Mayor Pam Iorio, officials put together a master plan for the park that envisioned adding some athletic facilities, maybe softball diamonds.

Buckhorn threw it out. Then he went in his own direction.

This summer, a Denver-based consulting firm hired for $708,400 interviewed residents and held community meetings to gather ideas for a new park. More than 350 people participated.

The resulting plan includes a 16,250-square-foot "river center" with upstairs community space, a terrace and panoramic views of Tampa's skyline.

Downstairs, officials propose a city-owned and -operated boathouse with space for 160 boats — not only for rowing and dragon boat teams that train on the river, but also for rental canoes, kayaks or paddle boards.

Buckhorn hopes the park makeover would take no more than three years to complete. So far, City Hall has set aside about $8 million for the project.

"I'm a third of the way there," said Buckhorn, who plans to run for a second term in March.

One source for additional funds could be future revenues from the Community Investment Tax, a half-cent sales tax for roads, schools and other projects. Buckhorn also will seek private money, maybe from selling naming rights to the river center.

Another thing that sets this project apart is its location — not quite in downtown, but across the river next to the working-class neighborhoods of West Tampa.

So plans include a history walk commemorating the area's past as Roberts City, a racially mixed neighborhood wiped out in the 1960s by urban renewal.

Officials also are thinking about naming the central lawn Phillips Field in honor of the neighborhood gridiron that was the site of black high school football games and Sunday gatherings during segregation.

"We need to be in a position where our history can be told over and over and over again," said an approving Pastor James Favorite at the nearby Beulah Baptist Institutional Church.

As expected, the plan calls for flattening the park's large earthen mounds — Buckhorn calls them "alien space mounds — to make way for an event lawn with views of downtown.

Residents, too, say the park's unusual topography hides what should be its best feature — its views of the river.

Even former Mayor Julian B. Lane's daughter said that before Tuesday's announcement, she had never walked to the river through the park named for her dad.

The new design is "a huge step in the right direction," Susan Lane said, adding that her father "would have been very pleased."

The plan also calls for a new splash play area, dog park, expanded playground, larger athletic field and new sand volleyball courts. The number of parking spaces would increase from 113 to 291.

A final aspect that sets this project apart is that it's just one piece of a larger vision for an area Buckhorn calls the "west river."

Buckhorn and Tampa Housing Authority officials are working on plans to redevelop an additional 120 acres, most of it government-owned, on the west bank of the river.

The area includes a city truck yard that could cost $17 million to move, as well as North Boulevard Homes, a World War II-era public housing complex that officials want to bulldoze and replace with a more traditional neighborhood with walkable streets.

To do it all, the city hopes to win a federal Choice Neighborhoods grant for tens of millions of dollars. Buckhorn said showing a commitment to invest in Riverfront Park might help the application.

Together, Buckhorn said, the park and the west river plan could create one of the most sweeping redevelopments in Tampa history — a possibility not lost on residents at a community meeting Tuesday night.

"If all of this takes place," said Sandra Niles, nodding toward maps and drawings on display at nearby Blake High School, "West Tampa is going to be a brand-new neighborhood."