The Caihong Waterfall (彩虹瀑布 [Cǎihóng Pùbù]; meaning "Rainbow Waterfall") was one that Mom and I had to work a bit for. While we technically only hiked around 1.6km round trip from the nearest parking area that we could find (which itself involved a dicey drive up a single-lane road; see directions below), the hike was steeply and relentlessly uphill. Given that our visit took place on a pretty hot, humid, and sunny day, it became quite a deceptively tiring hike. Since this waterfall was pretty much right above the Dongpu Hot Springs (I've also seen it spelled Dongbu Hot Springs), if ever there was a proper pairing between a waterfall hike and relaxing at a hot spring, I'd say this would certainly fit the bill.
Sadly, due to time constraints, Mom and I didn't engage in soaking in a hot springs here nor did we see any of the namesake rainbows despite the fine weather. What we did see, however, was a plunging 25m waterfall contrasting against blue skies with that on-top-of-the-world feeling after having climbed so high to get here. For all the effort it took to get up here, we were disappointed to see the area was spoiled by a huge mesh of pipes running before the main waterfall, and especially further downstream above an intermediate waterfall on the Bading Stream (八頂溪 [Bādǐng Xī]). This made us wonder if there was some water diversion going on with this waterfall to feed some of the hot springs in town further down the mountain.
Initially, we started hiking from the main road running through the town of Dongpu. We had doubts about being able to drive up a narrow steep road that began almost immediately from its turnoff deviating from the main road. But when we spent around 25 minutes of relentless uphill hiking along the mostly single-lane road, we saw that there were more parking spaces. And it wasn't until we reached a particular cafe (that wasn't open at the time) with a distant view of the Caihong Waterfall still way up the mountain did we decide that I should go back down the road, pick up the rental car, and make the drive up to the highest car park that we could get to. Once we did that, we then started the hike with the minimal amount of climbing left to do. Had we walked all the way up here from town, it seemed like the overall hiking distance would have been about 3.1km round trip with over 350m of elevation gain instead of around 1.6km round trip with over 200m of elevation gain.
So after leaving the car, we went through a little area between a handful of buildings before the foot trail picked up as the path ascended a series of steps leading up to what appeared to be a longhouse at the end of a switchback. The trail would continue its relentless climb while being mostly exposed to the sun as we made it up to a long and high suspension bridge called the Rainbow Suspension Bridge (彩虹吊橋 [Cǎihóng diào qiáo]) at a little over 400m from the trailhead. This bridge actually provided a little bit of relief from the humidity because there was a bit of a breeze that passed through. But the bridge also reinforced this top-of-the-world feeling as we could glimpse part of Dongpu way down below while the immediate gorge floor was also pretty far down below our feet. This was definitely not the kind of bridge to be on if you have a crippling fear of heights.
Beyond the bridge, the path continued to climb while weaving in and out of shaded and non-shaded areas. At around 200m, the trail skirted around an intermediate waterfall within what was apparently called the Lover's Gorge (情人谷 [Qíngréngǔ]). As stated earlier, the presence of a mesh of pipes or wires really took away from what would otherwise be a nice and relaxing spot. After another 100m of uphill walking along the Bading Stream, we finally reached the end of the trail where we were right before the Caihong Waterfall. At least with this waterfall, the pipes and wires were mostly alongside the lower parts of the Rainbow Waterfall, but we still thought they were eyesores.
As for the rainbow, our arrival to the falls at around high noon meant that we needed to be somehow higher up on the trail and looking more down at the falls. Since it wasn't possible to do that during our visit, I suspect that the more optimal time to see a rainbow would be later in the day when the sun would sink lower on the horizon. But that would mean that it would still have to be sunny towards the late afternoon, and the adjacent mountainsides must not block the sun's rays either. In other words, it seemed like that all the planets had to align in order for this waterfall to live up to its name. That was kind of a bummer, especially since things in and around Dongpu seemed to be named Rainbow this or Rainbow that while numerous walls and railings had rainbows painted on them.
Overall, Mom and I had spent about a little over an hour to do the last 1.6km round trip of hiking. I could have easily taken us 2-2.5 hours round trip had we walked up all the way from the town of Dongpu Hot Springs.
We were able to access the Caihong Waterfall or Rainbow Falls from the town of Dongpu Hot Springs (東埔溫泉 [Dōngbù Wēnquán]). The approach we took was from the north, where we passed through the town of Shuili (水里 [Shuǐlǐ]) before heading south to Dongpu. We'll focus on this driving route in this section. That said, from looking at the maps, it also appeared to be possible to drive east from Chiayi (嘉義 [Jiāyì]) to Dongpu via the Alishan National Scenic Area (阿里山國家風景區 [Ālǐshān Guójiā Fēngjǐng qū]) along mostly the Tai-18 highway. We can't talk more about that since we didn't do it though.
First, we had to drive to the town of Shuili. We managed to get here from the Shanlinhsi Natural Park via the Highway 151 then the Highway 131. It took us around an hour to make this drive. From Sun Moon Lake (日月潭 [Rìyuè Tán]), we would head south on the Tai-21 highway towards Shuili. If we were taking the National Expressway 3 from either Taichung (台中 [Táizhōng]) or Chiayi, then we'd leave the expressway at the offramp to get onto the Tai-3 highway. Then, we'd turn left and follow the Route 3丙 (the character is pronounced "bǐng") before continuing east on the Tai-16 highway all the way to Shuili.
Once we were in Shuili, we continued to drive south initially along the Tai-16 highway then south along the Tai-21 highway. We'd then continue along the Tai-21 highway (passing through a valley that appeared to have been affected by a severe landslide at one time) for about 25km turning left onto a road leading to Dongpu (called 開高巷 [Kāigāoxiàng]). Once on the Kaigaoxiang road (by now there were signs pointing the way to Dongpu or Dongbu), we drove another 5km before turning left at a junction with a traffic signal. We then followed this road for about another 3km. The turnoff leading up to the Caihong Waterfall or Rainbow Falls was on the narrow street to our left. If driving narrow and steep single-lane roads doesn't sound appealing, then you can find parking in town within walking distance from this turnoff. The drive from Shuili to here took us about an hour. However, if you're ok with continuing the drive to shorten the hike, read on.
So once we were on the narrow turnoff, we kept right at the immediate fork to start the steep and narrow climb. Given that the inclines were on the order of 15-20% grade, I'd recommend driving in low gear with the AC turned off. After another 100m, we turned left and continued the climb. Note that there were already a few car parks along this stretch. Anyways, we then drove an additional 600m before finally parking in a small lot near some buildings. This was probably as high as vehicles could go.
To me, the scary thing about the last 750m stretch wasn't so much the steep incline (though it could be nerve-wracking), but it was more so the single-lane nature of the road. That was because there were no pullouts for most of this stretch, and if there happened to be traffic coming from the opposite direction (there wasn't one during our visit, fortunately), then there would be no opportunities for the vehicles to pass each other. That would mean, someone would have to be willing to back up on the narrow road, and if you're not skillful in backing up on such a narrow and steep road, then there could be some scrapes to the car as well as delays. So this is the risk that we wound up taking, but I'd imagine it might not be a good idea if there would be more drivers here (like on a weekend).
Finally, for a little bit of geographical context, Dongpu was about 37km south of Shuili (about an hour's drive as mentioned before) or 64km east of the Alishan National Scenic Area (at least 90 minutes drive) and 124km east of Chiayi City. Shuili was about 16km south of Sun Moon Lake National Scenic Area (under 30 minutes drive), 46km north of Shanlinhsi Forest Park (between 60-90 minutes drive), 57km southeast of Taichung (over an hour drive), and 74km northeast of Chiayi City (under 90 minutes drive). Taichung was 168km southwest of Taipei (about 2 hours drive).
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