From the Long Lake trailhead parking, walk on the well-used trail to Long Lake through forest. Compared to the Mitchell Lake/Blue Lake trail, this Long Lake trail is in much better shape. The trail initially takes you near the lake outlet in about .2 mile. After that, it goes along the north shore, in the forest and stays well away from the lake. Follow the trail around the lake on the north shore for a mile to a trail intersection. Stay left here for the trail marked "Isabelle Glacier." Continue another mile on trail to Lake Isabelle staying on the north side of the lake. The trail gains elevation more steeply just before the lake, then follows close to the shore through some willowy sections and then climbs a little before dropping you back down through a rubble area back to the shore. Beyond Lake Isabelle, there are three successive basins with intervening, steeper sections to ascend. Just beyond Lake Isabelle, the trail ascends on some switchbacks next to a beautiful cascading stream. In the next basin, the trail meanders over to the south side of the basin, crossing the main stream and becoming somewhat lost in that section by following the stream course briefly. After that, the trail ascends up to the next basin which holds a small, unnamed lake at the foot of Shoshone Peak. By the time you reach here, most of the terrain is rocky with plenty of boulder-talus. In earlier season, expect to be mostly on snow from here on out. The trail to "Isabelle Glacier" will no longer be of use here. Continue WSW either off-trail or following faint climbers trails to a yet higher basin at 12,100 filled with more boulder-talus. Now, you are at the foot of Apache and Navajo and it's time to make a decision as to which of these two summits to climb first or which you'll be doing alone as a single peak day. You may also want to make mental note of "Airplane Gully" for future reference, especially if you plan on including Navajo in your plans for the day.
A note before continuing: In 1998, Gerry Roach published his book on climbing in the Indian Peaks, the year in which we climbed Apache and Navajo. If only we had known about that book at the time! We did this climb with very little beta to go on. With that said, our choice that day was to head directly up a snow-filled couloir that topped out just a little south of the Apache summit. This route has become known as the "Apache Couloir." We did this route about July 8th. The couloir was completely snow-filled. In fact, from Lake Isabelle on, we had been on snow most of the time. The couloir probably averages 35 - 45 degrees. Ice axe is mandatory. Crampons or micro spikes are welcome. We had only brought ice axes. The east-facing couloir will soften up quickly in the morning so step-making should not be a problem. Watch for a cornice at the head. You don't want that releasing while you're in the gully. The 1,000 feet of gain is just a long grunt. We rate it Class 2+ because you at least need to know what you're doing with an ice axe and how to handle yourself on steeper snow. Gerry Roach classifies this as a "classic" route. In mid-summer, surrounded by almost all rock and snow/ice, it certainly has an alpine feel about it.
Once you top out at the head of the couloir, it's an easy stroll over scree and talus to the summit just a short distance away. If you are averse to a snow route, then perhaps the easiest other way up is called the "East Ledges" route. Rated at Class 2+, the route begins in the same boulder-filled basin at 12,100 feet. (Snow filled in earlier season.) We returned in 2016 to climb Apache (and Navajo) by starting up this route. Head uphill in the direction of the large snowfield below the Navajo-Apache saddle. Some call this Navajo Glacier. A little below the snowfield, turn right (north) and follow a complex system of rock ledges to gain the south ridge of Apache not far from its true summit. In mid-July 2016, we could complete about 98% of this route off snow. Frankly, snow would have been easier than the talus. About mid way up, we found one very distinct ledge that we followed uphill to the north which deposited us on a slope of mostly broken rocks and boulders at times. We found it easiest to just head mostly directly straight up to the Apache south ridge. In essence, this ledges system just parallels the Apache Couloir on what will usually be exposed rock on the south side. The ledges consist of rock, some talus, gravel and boulder talus and some occasional tundra. Once on the south ridge of Apache, walk on easier but still rocky terrain, north to the summit.
Once on top, soak in the amazing view. To the east you see the broad expanse of the eastern plains of Colorado and much of the front range corridor. North and south, you see all the Indian Peaks summits and all the way into Rocky Mountain NP. To the west, you can see off toward Granby and the ranges beyond there. Now, make a decision as to whether or not to continue to Navajo Peak. If you do so, you need to be prepared for Class 3 scrambling, and a Class 4 ascent on Navajo. Some may wish to have a rope. If just heading back down, for those with ice axe and necessary skills, descend back down the Apache Couloir for an amazing glissade. If not skilled and/or somewhat terrified by such, follow the "East Ledges" route back down.
Links to other information, routes & trip reports for this peak that may be helpful.