Walkers won't have difficulty finding great places for day-hikes and longer treks in Italy. There are few fences keeping you out of places, and most everyone will know of an ancient trail their parents used to go to market, or a trail passing by their favorite forraging spots (these, as you might expect, are described rather vaguely). You'll find trail blazes all over Italy like the one you see on the right.
There are long distance walking trails in Italy, of course, but there is also a reawakening of the spiritual pathways like that of the Via Francigena, the "Frankish Way" from Canturbury to Rome.
And there are planned treks, like the ones proposed by mapmaker Giovanni Visetti. These are free, planned treks with detailed maps that you can do at your own pace. Each trek is mapped and elevations are graphed so that you know exactly what you're getting yourself into. Here is an example of the map for the "Path of the Gods" Sentiero degli Dei on the Amalfi Coast, with detailed instructions on the hike.
The Valcamonica - Great trekking, great rock art.
La Via Francigena - Spiritual walking on the pilgrimage trail to Rome.
A Path to Lunch - Walking trails and trekking in northern Tuscany and southern Liguria.
La Via Della Costa is a new route up the Ligurian coast that ultimately takes you to Santiago di Compostela. 350km in 12 stages.
Hiking Campania is a fabulous new site that includes not only maps and descriptions of walks and treks in Campania but a blog with a very evocative voice about walking and the cultural interactions you can have on an Italian walk. There are also guided walks available.
The province of Firenze (Florence) has set up a great site with trekking maps of the natural protected areas in the region: Aree naturali protette e sentieri in provincia di Firenze (in Italian).
Strada del Vino Colli di Candia e Lunigiana - A walk, mostly along the Via Francigena in the Lunigiana. What I like about it is that it's titled "A walk among marble and lard."
Puglia - The Foggia region has a nice Trail Map and Itinerary (look under "Materiali Promozionali" for links, or select the first one for a pdf with all of them). Also see an interactive map of Puglia.
Like markets? This Venice Rialto Walk explores the geographic heart of Venice, Italy.
Giovanni Visetti: Hiking Guide and Mapmaker - a good resource for walks and walking maps, especially along the Amalfi coast and the Island. of Capri.
Giovanni's spectacular maps will not let you down; his most popular you've probably heard of: Path of the Gods, Capri, Campanella, S. Costanzo, Valley of the Mills - Amalfi, Sirenuse Trail, Monte Faito, Sorrento. You can access them here with associated QR codes.
Walks on the Wild Side - A writer walks Basilicata, the region around the instep of Italy's "boot".
Walking with St. Francis - Walking around Assisi, in the footsteps of St. Francis.
The Via Francigena in Europe - What you need to know about the pilgrimage route from Rome to Canterbury. Also see, The Via Francigena in "The Valley of the Abbeys" from Initaly.com and our own Map of the Via Francigena.
Alpi Apuane Trials - Itineraries for walking in northern Tuscany, in Italian.
See Tuscany - Urban Trekking - Four urban treks around Siena.