The Rialto has been Venice's commercial district for centuries and it has a great sampling of historical sites. For example San Giacomo di Rialto said to be the oldest church in Venice is in this district.
The San Giacomo was the only building to survive a massive fire in Rialto in the year 1514 making it the oldest building in the district today.
There's also the Ponte di Rialto the oldest, and most celebrated of the four bridges that span the Grand Canal. It's one of Venice's most iconic pieces of architecture, so you'll want to cross it at least once.
The bridge as it is today has been in use since 1591, but it's actually been here in different forms since as far back as 1180.
The Ponte di Rialto was built in the first place to make it easier for Venetians to get to and from the popular Rialto market. Centuries later that same market is still going strong, and is now enjoyed by tourists as well as locals, and for good reason. The produce is fresh, and the seafood is even fresher. Buy some for a picnic, or just walk through the bustling market and take in the atmosphere.
The Rialto will leave you with a sense of the connection between Venice's past and present.