The old port is located just south of Old Montreal, along the waterway.
There is lots to see and do (especially for families). Montreal's science world, shopping, green parks, paddle boats in the lagoon, and bicyle and rollerblade rentals (with helmets).
In the evenings, there are often free concerts or open air theatre. When I was there, I saw a great performance (free) of Shakespeare's midsummer night's dream.
The Old Port area of Montreal is a classic, timeless beauty of cobblestone streets, charming boutiques and outdoor vendors. Fall in love, or rediscover yourself amongst a relaxed setting full of quaint nooks, winding pathways and trendy eateries.
Also in this area is the Aquabus (a yellow and blue bus that takes you on a tour of the old port area and then enters the river for a small riverboat tour, I recommend). You could also catch a romantic (yet sometimes overpriced) horse-drawn carriage through the old port area. Nearby is the famed Notre Dame de Basilique and funky little shops and bakeries.
Exhibitions, artists, concerts and more fun events frequent this area, so be sure to check ahead. Also stop by the Montreal Museum of Archeology, the Royal Bank and Montreal Science Centre. Take your camera! Plenty of gorgeous historic buildings.
The old riverfront has been meticulously restored and is bustling with restaurants, cafes, galleries, shops, harbor cruises, even a public space and an IMAX theatre.
The cobblestone streets with the occassional passing calèche (horse and carriage) adds a charm to the Vieux-Port. There are some tourist traps here (shops which overly commercialize T-shirts, maple candy and the Franco/Anglo linguistic wars), but there are also beautiful places to see and experience.
Gardens in the Old Port. I'm not sure of the name of the sculpture gardens in the Old Port, maybe it was 'MosaicCultures'?
The sculptures made of bushes and shrubs were fantastic. You can see much of the gardens by walking along the park, so unless you are very interested you can save the admission price.
The Old port along the St Lawerance River has been transformed from an industrial area into parks, shops and restaurants. Its a great place to get a bite to eat or to just roam.