The two sounds occur almost simultaneously: Just as my cellphone alarm begins its melodious chime to rouse me from sleep, the dark clouds above my guesthouse in the town of Tanabe on the Kii Peninsula burst forth with a pounding rain. Within minutes, it’s clear that my plans of spending three days hiking the Nakahechi branch of the Kumano Kodo pilgrimage trail have quite literally gone awash.

A quick post-breakfast consultation with my fellow hiking partners, James and Felicity, confirms our cancelation. With rain running in rivers in Tanabe’s streets, we quickly re-evaluate our long weekend. Luckily, Felicity has visited the area before and it’s not long before we’re steering her car south in search of Wakayama Prefecture’s best onsen (hot spring).

Our first stop is along the coast near Shirahama, where we veer off down a tiny alleyway before braking just in front of a seawall. Only a small sign on the cement wall indicates that this is Saki-no-yu, a 1,300-year-old onsen that was once the beloved destination of the eighth Tokugawa shogun, as well as several emperors from the Asuka (538-710) and Nara (710-94) periods.

“Even modern celebrities come here to bathe,” says Motoshige Nishimura, the onsen’s genial caretaker who was appointed to the job two years ago by the local tourism board. However, he assures us, they get no special treatment and share the space with whomever happens to be visiting that day.

There aren’t many people at all (and certainly no movie stars) soaking in the waters when we arrive and we enjoy stunning views of the slate-colored sea with only a handful of other people. The baths are built as terraced steps leading down to the water, the hottest of them situated at the top. Every now and again a large wave sprays over the lip of the rock wall at the bottom pool, dousing everyone within.

For a post-hot spring snack, we walk up the street a few hundred meters to grab an onsen tamago (lightly poached egg). Boiled in the same source of water that we have just enjoyed ourselves, the soupy eggs provide a great protein pick-me-up and we purchase a few extras to fuel us for the rest of the day’s explorations.

Sunday morning dawns much the same as the previous day and instead of tackling the trails, we once more find ourselves in search of a good soak. A five-minute ferry ride deposits us in front of the foyer of the Urashima Hotel. The massive building is initially off-putting. Given my predilection for more intimate onsen, the opulence of the Urashima makes me uncomfortable. The long hallways resemble airport concourses and it takes a good 10 minutes to reach the baths.

My fears are instantly allayed as the door slides open to reveal a series of pools in a dimly lit grotto. Water drips rhythmically from the ceiling and the pounding of the surf on the rocks at the far end of the cave is audible even in the changing room. We’ve just missed the morning rush — the hotel’s guests were all clustered at the checkout desk — and the cave is empty save for ourselves. Before we can be disturbed, Felicity and I head straight for the small pool at the cave’s edge. The grotto’s only opening is here and the waves we could hear earlier can now be seen through the gate, crashing onto the rocky coast. Despite the ocean’s intensity, it’s a hypnotic sound and both our minds and our muscles can’t help but unwind.

The sky is clearing slightly as we take the ferry back to the peninsula proper and turn north to head into Wakayama’s mountains. The narrow road cuts through a misty valley, where icy cataracts tumble down the steep slopes and tiny villages fade in and out of the fog like Brigadoon.

The clouds have caught up with us once more by the time we reach Kawayu Onsen. Thankfully, the precipitation manages to hold off as we pick our way carefully across the rocks to the edge of the Ohtou River. Removing our footwear, we wiggle our feet down into the silt riverbed. Warm water bubbles up into the pool we’ve created, making the perfect do-it-yourself footbath. Unlike other prefectures in Japan, Wakayama’s hot springs aren’t the result of volcanic activity. Rather, it’s believed that a fissure in the tectonic plates under the Kii Peninsula results in geothermal reactions. In Kawayu, locals have put this unique occurrence to good use by creating a massive rotenburo (open-air bath) on the banks of the Ohtou every winter. More than 1,000 people can cram into this mixed-gender onsen (bathing suits required). As we’re still a bit too early in the season, we have to do our own digging but the trade-off is having the river almost entirely to ourselves.

Just up the road, we end our day at Yunomine Onsen. Little more than a hamlet, this mountain hideaway is home to one of Japan’s most notable hot springs, the UNESCO World Heritage site of Tsuboyu. Consisting of no more than a little shack over a section of the local river, the unknowing observer wouldn’t give it a second glance. However, its reputation as a healing spring has assured it a place in the pantheon of Japanese pilgrimage spots. Legend holds that 15th-century lord Oguri Hangan was brought here by his beloved in an attempt to cure him of severe deformities caused by a poisoning. A dip in the springs restored him to full vigor and Tsuboyu’s praises were sung far and wide.

So popular is the onsen these days that a rather ineffective reservation system is in place, allowing each party up to 30 minutes in the boiling waters. Time slots are not officially determined, as the water’s scalding temperature causes many to cut their visit short, and guests are simply required to wait around until their number is called. Despite repeated efforts on the evening of our arrival, we miss out on the last of the day’s available slots and are advised to turn up at dawn to try again. Disappointed, we console ourselves with dinner at Minshuku Kuraya, our evening’s accommodation. Third-generation proprietress Takeko Kuraya lays out a not insignificant spread, with the bulk of it coming from her garden out back. We feast on locally sourced deer sashimi, the Wakayama specialty of mehari zushi (rice wrapped in pickled mustard greens) and various vegetable and tofu dishes. The minshuku’s bath is more than acceptable, but we still hold out hopes for Tsuboyu in the morning.

It’s difficult to tell what the weather will do on our final day, as Felicity and I are up and in line at the Tsuboyu reservation kiosk before the sun even has a chance to rise. Our dedication pays off and we’re seventh in line for the famed bath. After breakfast, we settle in to wait on the wooden bench just outside Tsuboyu and by 7:30 a.m., we are entering the celebrated shack.

The water of Tsuboyu’s tiny pool allegedly changes color seven times a day. At this hour, it flits between aquamarine and turquoise, a far cry from the hue of the river just beyond the flimsy wood walls. I use the small paddle in the shed’s corner to churn the water in an attempt to cool it and make it bearable for our slightly chilled limbs. Sinking into the pool, I stick my legs straight out as Felicity instructs. Immediately, an eerie sensation washes over me, as my appendages seem to float out the back of the cave toward the river beyond.

The sun is shining brightly as we emerge from the confines of the tiny bath, the first sign of good weather we’ve had all weekend. We grab our hiking boots and packs from the guesthouse and set off on the trail to Hongu Shrine. I’m not sure what this change of adventures holds, but as long as there is an onsen at the end of the day, I’m game for anything.

Getting there: Trains run from Kyoto and Osaka to the city of Shingu on the southern coast of Wakayama Prefecture. Buses also run along the entire coast and to several spots on the Kumano Kodo pilgrimage route. Saki-no-yu (¥420 )is open every day but Wednesday from 8 a.m.-5 p.m. The ferry to the Urashima Hotel is free but the price of admission to the baths is ¥1,000. Tickets to Tsuboyu are ¥770 per person; only two adults will fit in the bath. For more information on hiking the Kumano Kodo, visit www.tb-kumano.jp/en.