Cerro Placas is a high peak in the Cajun del Maipo region of central Chile, just east of the capitol city of Santiago. At 15,328 feet in elevation, and being so rarely ascended it makes for a great climb for those looking to get off the beaten path. Very few people from outside Chile have ascended this peak as it's barely known by the locals, however, nearby Cerro Arenas is much more known to the local climbers in Santiago, as there is a beautiful multipitch rock route leading to this slightly lower sub-summit of Cerro Placas. Despite Cerro Arenas being lower, it is the most impressive peak you see on the drive and approach hike in, as Cerro Placas cannot be seen until you have reached the high camp.
From Santiago Chile, you will have to likely rent a car to get here, as there is no bus service up to the far reaches of the Cajun del Maipo roads (such as to the Alto Maipo mine, Elbalse el Yeso or the Valle de Colina Thermas). Buses more or less end shortly beyond the popular town of San Jose de Maipo at San Gabriel. Hitchhiking is an option too if you're open to it. Beware if you rent a car anyhere in South America, you know how to drive a manual, and you are comfortable driving in cities where the rules of the road are loosely followed.
Drive through the insanely touristy San Jose de Maipo and continue past the San Gabriel police guard house (I've actually never seen anyone there) and continue driving east, passing the left turn towards Embalse el Yeso. Pavement ends shortly after this junction and you'll continue up the steep gravel road with haul trucks running up and down all the time from the heavily disputed Alto Maipo operation. Just after the road crosses to the north side of Rio Volcan over a bridge, turn left and follow a series of wide switchbacks and park at the end of the improved road, right where the main road continues into the Alto Maipo work area. You can park at the large open area just before the roads enters the work area, elevation 2450 meters, which is closed to non-workers. Or with a 4WD, you can continue left up the steep, rocky jeep road that skirts around the west side of the operation and into the wide flat valley above and parking at 2600 meters.
From the lower parking area, simply walk the 4WD road to the start of the wide valley above, and leave the road when it turns back to the west. Hike north across the valley, fording the stream. Continue aiming northward to the SW facing slopes below the steep south face of Cerro Arenas. You will notice an old road switchbacking across this slope however it jogs really far to the right, and is so overtaken by rock slides it's no longer much use. Simply hike straight up the questionalbe talus/scree a bit to the right of the steep waterfall, and emerge on a beautiful flat grassy bench at 3000 meters. This would be a great place to camp if you were climbing the south face of Cerro Arenas, however is still a bit far from Placas. Continue north up the narrow valley to about 3400 meters, where a remnant bit of ice will provide a trickle of water even in March (it'll be a bit dirty though). Just below this small ice patch is a nice flat and improved camping spot, the only decent place to camp above the grassy bench 400 meters below.
From this nice camp spot, you'll ascent the west facing slopes to the right, which is nothing more than a bunch of scree (early season there will be snow). It's a grind up the slopes, but there is occationally some solid rock you can scramble on. At 3950 feet reach another flat talus basin offering a good rest spot before finishing the last 750 meters more or less up the SW face, weaving around cliffs following the talus slopes (or rock ribs if you're up for some slightly solid class 4). Reach the south ridge at 4560 meters where it flattens for a bit and continue north towards the summit. The final scramble to the top is class 4 where the route jogs to the left (west) side of the crest when a steep step must be bypassed, or maybe there's a class 3 route when it's completely dry but we had to contend with a dusting of fresh snow.
Cerro Arenas can also be linked with Cerro Placas bu following the connecting ridge south when you reach it. For those with the technical know-how, consider the south face though.
No red tape, other than the Alto Maipo of course...simply go around the work area.
Can be climbed anytime of year I guess, September-January will have more snow coverage, while February through April it'll be bone dry. May-August...I don't actually know how harsh winters are in this area.