The Esplanade is known as one of Boston’s defining parks, a graceful stretch of tree-lined paths and grassy banks alongside the Charles River that draws millions of visitors each year.
Now, supporters are seeking to transform the riverside greenway into something grander still.
In a sweeping plan two years in the making, The Esplanade Association unveiled a blueprint yesterday for the 3-mile park that envisions a pedestrian walkway jutting out into the Charles River, an expansive terrace near the Hatch Shell, and a widened bridge over Storrow Drive that would serve as a gateway to the park.
‘‘It’s a vision for what the park could be,’’ said Sylvia Salas, executive director of the nonprofit group, which raises money and cares for the Esplanade.
The group is also considering large-scale projects such as replacing the parking garage for the Museum of Science with a walkway along the river, or building a Ferris wheel akin to the London Eye.
The association’s recommendations represent the most far-reaching effort in recent memory to refurbish the park and, while preliminary, they call for broad renovations. The park, world famous as the scene of the city’s July Fourth celebration, extends along the Boston shore of the Charles from the Museum of Science to the BU Bridge.
A committee of planning specialists, assembled by the group, held numerous public meetings to complete the blueprint and worked closely with officials from the state Department of Conservation and Recreation, which manages the land and would be responsible for the cost of renovations.
Edward M. Lambert Jr., the department’s commissioner, said the state needs as much as $2 billion to pay for overdue maintenance at its parks across the state.
The group’s plan was presented last night to an audience of some 200 people at the Boston Public Library.
Lambert said he is optimistic that the state can afford improvements if nonprofit groups help fund a portion of the renovations.
‘‘With these properties come an added value to the quality of life that none of us would want to do without,’’ he said at the meeting.
Calling the recommendations a vision for the park, the friends’ group stressed that the proposals are meant for wide public debate and said the more ambitious ideas would take years to materialize. The blueprint did not provide cost estimates or a time frame for the renovations.
But in drawings that accompanied the report, the scope of the plan becomes clear. A stretch of path beside an overpass, now nondescript, juts out over a part of the river, with water on both sides, while a bike path runs parallel.
A second image shows a tall windowed cafe with outdoor tables in the shade, and another depicts a large terrace by the Hatch Shell with an information booth. An aerial view shows a widened bridge across Storrow Drive lined with vending booths, serving as a grand entrance to the park.
If these images become reality, the park would feature new lagoons and sitting areas around a refurbished memorial to Charles Eliot, a 19th-century landscape architect. The Boston University sailing pavilion would reopen as an indoor facility for visitors, the long unused Lee Pool would reopen, and new playing fields would be installed.
The plan also calls for extensive landscaping improvements that could be more immediate and in many cases are long overdue, Salas said.
‘‘People look at the park and think it’s beautiful, but if you spend more time there you realize the grass is patchy, and the soil is like concrete,’’ she said. ‘‘There are pathways that need to be better planned and monuments badly in need of repair.’’
Granite landings built in the 1930s, popular overlooks for visitors, are ‘‘crumbling into the river’’ after years of neglect, she added.
Officials hope to add signs that highlight the park’s history and provide directions between the Esplanade and the city proper.
Besides improving the park, the association also wants to reclaim land lost to Storrow Drive over the years by expanding onto tunnels and reconfiguring the road under the Longfellow Bridge.
The overall planning process took flight two years ago, when the Esplanade marked its centennial.
‘‘We really felt it was a perfect time to start looking at the park comprehensively,’’ she said.
On the Esplanade yesterday afternoon, bikers, runners, and the occasional walker took advantage of the mild weather and offered some improvement ideas of their own.
Emma Harding, 32, of Cambridge, liked the idea of a cafe at the Hatch Shell to liven up the area.
‘‘It would be good to see that space be a bit of a social area,’’ she said. ‘‘It just seems like an empty space.’’
Adding lights at night, she said, would help give the area some ambiance.
Paul Lazareth, 50, of Cambridge, said he loves virtually everything about the park he rides his bike through every day, even if the path’s bumps and dips are tough on his tires.
But additional bridges across Storrow, he said, would allow even more people to enjoy the open space.
‘‘I feel bad for some of the people who can’t make it over as quickly,’’ he said.
As if he had received an advance of the report, Lazareth said he would also update the informational signs along the path that seem out-of-date.
‘‘History is great, but they’re not written very well,’’ he said.
Sarah Chung, 30, of Brookline, said she rides her bicycle on the Esplanade whenever she can. She recommended wider paths or designated bicycle lanes and agreed with other regular visitors that getting to the park should be simple.
‘‘It’s like a world away,’’ she said from a bench by the river. ‘‘But it’s right here.’’