The First Flatiron is a true slab-climbers paradise. It's not as popular as the more famous Third, but it is larger, is open year-round, and has a greater variety of routes. For those looking for a shorter outing than the stellar Direct East Face (5.6) route, and something a bit more challenging than the North Arette, Fandango is a great choice. It reaches the summit ridge in 4-5 pitches joining the rest of the popular routes, then rappels 100' in an easy single pitch to the west bench.
Approach Fandango as you would any other route on the First. From Chautauqua, head up either the Chautauqua Trail or the Mesa Trail. Follow signs for climber access to the First up a steep but well-maintained trail. When the main trail reaches the base of the rock, turn left and continue up the well-marked trail as it switch-backs away from the First and across a large talus field.
When the trail approaches within 10' of the rock, scramble down to the face. Technically, this spot is the start of Bakers Way (5.4) and Fandango starts about 100' below you down a 3rd-class gully along the base of the face. See below for an alternate start.
This description assumes you have scrambled down 100' or so from the trail. The route starts about 50' left and up hill from a large, left-facing dihedral system.
Climb a set of shallow flakes and features to a roof.
Traverse left about 80' under the large roof before turning upward for another 80' to a small tree with a sling anchors. Watch for horendous rope drag under the roof and place directional placements to protect your second from a long swing.
instead of scrambling down the base of the rock, start from about 15' off the trail and climb one pitch to the small tree left of the large roof. This shortens the climb by one pitch and avoids the first two standard pitches which aren't all that interesting anyway.)
Work your way up and right from the tree on easy terrain following the line of the large, left-facing dihedral/chimney/ramp. Pull a short roof to the right of a large tree and set up a belay near the dihedral.
Follow the dihedral up steeper terrain below a large roof. At the roof, turn left and ascend to it's leftmost edge. Belay where possible.
Climb beautiful sandstone following a shallow and discontinuous fist crack about 5' left of the large dihedral to the ridgeline. The route joins the ridgeline just below the "quartz crystal pitch" or the third highest tower on the summit ridge (the penultimate false summit).
Once on the ridge, follow it up and over two false summits to the true summit. The terrain here is relatively easy except in a few spots, but rope drag and the potential for pendulum swings will keep you on your toes. Surmount the final summit block by making a few committing moves up an overhanging chimney or moving right into an easier gully directly below the rap bolts.
Rappel 100' west from a pair of large bolts on the summit. A single 60 meter rope will make it easily, a 50 meter rope will probably not. Alternatively, scramble down to the southeast along low-fifth-class terrain. Hike south and east on the trail between the First and Second Flatirons back to the base of the rock.
A standard Flatiron rack is sufficient here: a set of medium-large stoppers and cams in the 1"-4" range. Bring long slings to tie off natural features. Flatirons climbing tends to be pretty runout, so don't be surprised if you go for 30' or more between gear in the best of circumstances! Long ropes will make the trip faster; a single 60 meter rope is required at the very least to rappel from the summit.