Pergolas are similar to arbors but larger wooden, or vinyl structures that provide a light, airy inviting space to define an outdoor room for socializing, dining, or just to relax. They are free standing structures with no walls, and cross rafters for its ceiling/roof. However they may be attached to your home to create an extension to your outdoor living area, or as a pathway between structures.
You can naturally enclose them by planting aromatic flowering plants that vine, to climb up the pillars and intertwine through the cross rafters. Or, you can be creative with all-weather fabric and drape it from one post to the next adding a soft flowing and romantic effect. Also, add some hanging flowering planters around the pergola for additional wall definition. When positioning your pergola take into consideration the following: the time of day, and angle, at which the sun shines; account for the season(s) as well; and any possible additional shade coverage of the area.