Many of Boston's most ambitious and expensive construction projects have stalled out, leaving behind unsightly construction sites. The Boston Globe has asked architects for their ideas for making the sites more useful and attractive.

The Globe asked 20 architects and firms for their ideas on sprucing up the currently vacant sites, prompting ideas for parks, makeshift movie theaters, and even an algae reactor. Below are the 11 proposals for the Filene's redevelopment, but The Globe also attracted proposals for the currently defunct sites at the Columbus Center, Longwood, and the Harvard Science Complex.

Re-imagining Boston's stalled projects [The Boston Globe via Archinect]

Design #1 — Design firms: Howeler + Yoon Architecture and Squared Design

The team proposes to build a vertical algae-powered bioreactor on the Filene's site.

Design #2 — Architect: Michael Joyce

Design firm: Goody Clancy Associates

Joyce proposes to build an aluminum scaffolding on the site to hang replicas of suits to evoke the history of the Filene's site. At night, the suits are presented in silhouette and backlit lit by vintage images of the store's sale staff and customers.

Design #3 — Design firm: Neoscape

Neoscape proposes to build a large video screen on the Filene's site that would allow passersby to control the content from a touch screen installed on a fence on the site's perimeter.

Design #4 — Designer: William Frese

Frese, who is a scuptor, proposes to turn the Filene's site into an abstract apothecary chest, evoking the neighborhood's history in the jewelry trade. The "jewels" and a jeweler's hand tool would be placed throughout the site.

Design #5 — Designer: Brad Koerner

Design firm: LAM Partners Inc.

Koerner proposes draping the Filene's site in enormous fabric that would serve as the canvas for supersize LED video screens. The screens could project any number of animations, such as a waterfall, or artists could be commissioned to produce animations that reflect the spirit of the Downtown Crossing area. Flood lights would accent the remaining portions of the structure.

Design #6 — Architect: Travis Ewen

Design firm: Carol R. Johnson Associates

Ewen, a landscape architect, proposes to create an urban garden on the Filene's site with wind turbines and solar panels to be supported by the existing buildings.

Design #7 — Designer: Dave Waller

Design firm: Brickyard VFX

Waller proposes to use the empty Filene's site to post vintage neon signs from New England's history, featuring signs from old drive-ins, Howard Johnson's, and Dunkin' Donuts.

Design #8 — Architect: Derrick Choi

Design firm: XChange Architects

XChange proposes to erect a massive projection screen on the Filene's site to cover the buildings in images of Boston's sports triumphs and other celebrations such as Fourth of July and First Night. The construction site itself could be used to host a number of public-related purposes, such as the Boston Public Market farmer's market, Christmas tree sales, and the like.

Design # 9 — Design firm: Utile Inc.

Utile Inc., an urban planning firm, proposes to install crisscrossing boardwalks across the Filene's site that would provide new shortcuts through Downtown Crossing. Below the boardwalk would be a manicured pasture fit for sheep and other livestock that used to roam the nearby Boston Common.

Design #10 - Architect: Cynthia Bubb

Bubb proposes a bike park on the Filene's site, along with a large projection screen to show movies at night.

Design #11 — Architect: Christopher Golden

Design firm: Carol R. Johnson Associates

Golden, a landscape architect, proposes to fill the void in Downtown Crossing with a waterfall and urban oasis. The waterfall would drop from the side of the Filene's building and cascade into a swimming pool, which would be surrounded by a sandy beach. At night, lights and music would emanate from the core of the Filene's building.