Bird Island Pier is a long, narrow walk out between the Niagara River and the Black Rock Canal. It is a simple piece of waterfront infrastructure, but the views make it worthwhile: Lake Erie, the Peace Bridge, passing water, and Buffalo's skyline behind you.
Go in good weather and stay on the improved path. Wind can be fierce and the outer breakwall is not a casual stroll, but the accessible section gives Buffalo one of its better low-key walks by the water.