On Lewis your walking is limited only by your imagination, and your ability to read a map and navigate. A coastal path along the West Side of the island passes within a very short distance of Dollag's Cottage and provides easy walking along the coast. Bridges have been built along the route where rivers must be crossed and picnic tables are provided in several places. You could elect to walk all the route or just walk short sections depending on your inclination. The route skirts along the shoreline and crosses the sandy beach at Shawbost about 5 minutes walk from the cottage. Whales may be seen off the shore while otters are often seen on some of the freshwater lochs along the route.
The more adventurous might chose to walk the costal path from Tolsta, about 11 miles north of Stornoway, to Ness. This area is much more difficult walking requiring some ability with the map and compass and is certainly not suited to those with no experience at all. However it reaches across some of the most remote and barren country in the UK and there is lots to see along the way.
For those who don't like to follow a path then you can, basically, start from anywhere and go to anywhere. The population of Lewis is relatively low and clustered along the coastline and so the walker is free to venture across all of the interior of the island with a very low probability of meeting another person even for many days of wandering on the moorland. It goes without saying that such wild walking isn't suitable for everyone and it requires a high level of ability in navigation if the walker is not to become lost. Much of Lewis is relatively flat but of a rolling nature and so the horizon may be only 100 or 200 yards away with all around absolutely featureless. On the other hand there is nothing to beat the feeling of freedom and isolation as you drop into the heather by some remote Lewis loch knowing that there may not have been anyone sitting by this loch for many years.

Some walks in the area around Dollag's Cottage.

Winter walking close to Dollag's Cottage
Dollag's Cottage @ 7 South Shawbost
moorland near Uig on the Isle of Lewis
Panorama of the West Side of the Isle of Lewis
The Barvas Hills
Arnol moorland on the Isle of Lewis
Disused shieling on the Lewis moor
Uig hills from above Loch nan Geadh
View while out walking
Some of the most remote country in the UK