Downtown needs 'shopping' but not Belk's or Dillard's or things like that.
Downtown needs 'touristy' shopping. The night life is coming along great (ate at Wintzell's last friday, and was floored by the number of people actually out and about, it was awesome), but now that needs to be expanded.
DT needs things to keep tourists and conventioners interested during the day and on the weekends. If you've ever been to Charleston or Savannah, you know what I'm talking about, and that's what Montgomery needs to aim for.
My proposal is an open air market on the lower half of Commerce, between the street and current parking lot/proposed green space. Right now, there is nothing to draw people down towards the Riverwalk except a long, dark tunnel.
Charleston has an awesome open air market that is a huge draw.
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Now, imagine something like that on lower Commerce. Filled with local vendors, fruit stands, etc...
Now you've got something to draw people to the green space between there and the Embassy and Train station, as well as drawing them towards the Riverwalk.
You could even do a two story, with offices/apts/shops on the top, and market underneath.
At a few plaques and murals about cotton and slave trade and you've got a built in draw.