This city park contains not only a riding arena and a perimeter trail for equestrians, but also a children's farm area that features riding programs for kids. There are also extensive picnic facilities.
Of the trails within the park, only the perimeter loop is open to horses, but it is a pleasant ride through wooded areas, and connects to the Powerline Trail that leads west to the Sammamish River Trail and, someday, east to Redmond Watershed Park (currently you can ride there via a road-ride).
To get to the parking for horse trailers, nearest the arena, follow the end of SR–520 onto Avondale Road, after approximately 1.5 miles turn right on NE 116th St then right on NE 196th St, entrance to the park is near the end of road on the right.
Open
Length: ~2 miles
Surface: dirt, gravel
Share with: hikers, joggers, children
Restrooms, arena, picnic areas, children's farm
Parking for: 6+ trailers
Redmond City park:
http://www.redmond.gov/cms/one.aspx?portalId=169&pageId=4101
Map:
click on the "Park & Trails" link on the Redmond Park page, above.