Passing across the Mystic River drawbridge from Groton to Stonington, or vice versa, is a little like stepping through the looking glass: You're in the same village but also in a completely different place.

The side of Mystic that is located in the town of Groton, because of decades of careful stewardship, good planning and the diligence of an attentive Historic District Commission, is charming, vibrant, scrupulously maintained and a remarkably complete representation of an early New England village.

The Stonington side is, by comparison, a hodgepodge of conflicting building styles and intrusive outsized commercial development, from little strip malls to gas stations.

This is not to say Stonington's Mystic is not a nice town, with many responsible homeowners and businesses who make it such an interesting and lively community.

But, in terms of appearance, it is also the bedraggled and gap-toothed relation to its polished and refined cousin across the river.

Don't take my word for it, cross the bridge, behold the mishmash of buildings, empty lots and conflicting architectural styles on the Stonington side and compare them to the pristine, curated streetscapes in Groton.

Groton would never have allowed a strip mall with a fake lighthouse on one end, like the one in the heart of Stonington's Mystic. That's the big picture. But details are important, too, and Groton also wouldn't allow a faux historic building like the one going up now on East Main Street in Stonington to have modern picture windows across the front.

You can literally see how people react to these different atmospheres, if you visit on a busy spring or summer weekend.

The tourists are strolling shoulder-to-shoulder on the sidewalks of the Groton side of Mystic, window shopping and drifting in and out of bars and restaurants at the storefront level, all laid out in the same scale. If you blur your eyes, you might picture on the very same block women in street-length dresses and men in top hats.

The accommodating physical layout and beauty literally draw you in.

The sidewalks on the Stonington side are noticeably less busy, with storefronts and restaurants haphazardly spread out, and walkers seem headed either to the charming side, across the river, or on their way back from there, to their parked cars. An exception is the popular Mystic River Park.

Mystic tourism overall is driven by a few big generators: Mystic Seaport Museum, Mystic Aquarium, Olde Mistick Village, conveniently situated at Interstate 95, and downtown.

I would suggest it is the charming Groton side of the downtown that attracts visitors. Stonington downtown Mystic feeds off Groton Mystic. If Groton Mystic weren't there, a tourist might drive right past Stonington Mystic. You probably wouldn't drive some distance to visit it, anyway.

A lot of these differences are the result of generations of different approaches to planning and development in the two towns. No doubt the biggest factor distinguishing the two sides of the same village is the Historic District Commission in Groton, which regulates everything from siding material to window sizes.

It is alarming, though, that the differences in approach to planning and development on the two sides of the river appear to be accelerating.

The plans by the Whaler's Inn to replace a contributing building on the National Register of Historic Places, which they've already torn down, with a parking lot, enabled by the town, is an affront to anyone who cares about historic Mystic on either side of the river.

It is a planning crime that Stonington, a town with so much remaining historical character, doesn't at least have an ordinance that requires a waiting or warning period before a building may be torn down.

Indeed, the current Stonington administration was planning to tear down a contributing building on the historic register, one owned by the town, until the state moved to stop them. These same crimes against historical buildings shrugged off in Mystic would never ever be allowed in Stonington Borough, with its own planning board. It's a Stonington double standard.

Stonington's enabling development to forever change the future of its side of Mystic is about to go into overdrive, as plans for the biggest development proposed there in generations are unveiled.

This could go very badly.

Everyone should pay a lot of attention.

This is the opinion of David Collins.

d.collins@theday.com