With high-rises already planned within blocks of Denny Playfield, the last large, privately held green space in Seattle’s South Lake Union now could become a high-rise, too.

Vulcan, which owns 60 acres in the neighborhood, will discuss its preliminary plans for a 400-foot residential tower and 240-foot office tower with the city’s Design Review Board on Wednesday night. The meeting is 6:30 p.m. at the Queen Anne Community Center at 1901 First Ave. W.

The 1.8-acre site, bounded by Denny Way and John Street and Ninth Avenue North and Westlake Avenue North, is one of the most visible corners in South Lake Union, kitty-corner from a Whole Foods grocery store and just east of Denny Park.

Vulcan, owned by Microsoft co-founder Paul Allen, has led the transformation of a sleepy industrial area into a vibrant mixed-use district for tech and biotech firms.

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The changes accelerated in 2008 after Amazon.com signed long-term leases to move its global headquarters to South Lake Union starting in 2010.

Allen’s ownership of land in the neighborhood dates back to the early 1990s, when a committee was formed to promote the idea of creating the Seattle Commons, a 61-acre park along Westlake Avenue North stretching from downtown to Lake Union ringed by research-and-development firms. Allen loaned the committee $20 million to start buying land.

But after Seattle voters rejected a tax levy to pay for the Commons, Allen took back 11.5 acres and quickly assembled large swaths of additional land to undertake a privately led revitalization project focused on commercial uses.

The block under review — which the Commons committee acquired in 1995 for about $4.3 million with Allen’s loan — features a basketball court, playfield, parking lot and the South Lake Union Discovery Center, a showcase for Vulcan’s neighborhood plans built in 2005.

According to public records, Vulcan could pursue two options:

• A mixed-use project with a 420,000-square-foot office tower at the corner of Westlake Avenue North and Denny Way and a 500-unit residential tower at Ninth Avenue North and John Street. This option, which includes 800 underground parking stalls, would require the city to give up a public right of way.

• A commercial project with 570,000 square feet of office space in two buildings, with 600 underground parking stalls.

Both options would include 30,000 square feet of street-level retail.

Vulcan and its two architecture firms on the project — ZGF Architects and Ankrom Moisan Architects — envision the block as a future “retail destination,” a gateway to South Lake Union from downtown and a way to promote the Bell Street to Elliott Bay corridor.

The developer has proposed a pedestrian midblock walkway that would span from Westlake Avenue North to Ninth Avenue North. If the city grants Vulcan the right of way, loading docks would go underground instead of on the surface.

Vulcan declined to provide details on its proposal.

One of the region’s most active developers, Vulcan has built about 5 million square feet in 24 buildings in South Lake Union, and made national headlines in 2012 when it sold Amazon.com an 11-building portfolio for $1.154 billion.

The developer is constructing several buildings, each more than 300,000 square feet, that touch Ninth Avenue North and are leased to Amazon. A two-building complex called Phase 6 between Mercer Street and Republican Street is expected to be completed this year. Phases 7 and 8 are to be finished in 2015.

Sanjay Bhatt: 206-464-3103 or sbhatt@seattletimes.com On Twitter @sbhatt