WARNING: As the park service and all the books say, DO NOT ATTEMPT TO HIKE TO THE RIVER AND BACK IN ONE DAY.
Unless...
You've researched and planned well and trained for months. See my specific advice below.
For me, it was fantastic.
April 27, 2022
5:15 AM start at the South Kaibab trailhead Didn't actually need my headlamp, but had it with me, because...be prepared.
Enjoying sunrise from Ooh-Ah Point and downward:
Onward and upward (1000 feet up on the exposed switchbacks of the Devil's Corkscrew, to be precise). Resting near the top, I met my second mule train.
The section of trail from Indian Garden to 3-Mile Rest House (and partway to 1 1/2-mile Rest House) was actually the sunniest and hottest for me, so next time I think I'll wait at Indian Garden until the cliffs shade the trail. But the full sun provided some nice, unshadowed views:
Only 1.5 miles from the top, I started feeling a bit nauseated, so I slowed down even more and took breaks literally every 10-15 minutes, sipping Pedialyte and nibbling Fritos, until I felt better. I then met some Aussie friends from lower on the trail and we walked together, chatting about our travel and our favorite mountain climbing documentaries, and before I knew it, we were at the top!
1) You're in good hiking shape.
2) You go in spring or fall while it's not too hot. Remember that it's about 20 degrees hotter at the river than it is at the South Rim, and large sections of the trail have little to no shade. DO NOT ATTEMPT this entire hike in one day in full summer, now matter how tough you think you are. I consider "full summer" in the inner canyon to be roughly late May to late September, depending on the year. If you think you don't need to worry about the heat because it's "a dry heat," be sure to spend plenty of time hiking in this dry heat before you discount it.
3) You've trained over the previous few months for this specific hike by taking:
-a few long hikes (12-16 miles) while wearing the fully loaded pack you plan to use
-several hikes that exceed 3000 feet of elevation gain, preferably a couple that exceed 4000 feet
-at least one high-elevation hike (at least 6000 feet)
-one or two hot hikes ("feels like" temp of 90+) to see how your body reacts
-at least one canyoning hike (where you go downhill first and uphill second)
4) Wear well-broken-in hiking boots/shoes.
5) Research the trail, how to keep your energy up, and what to pack. Going light is good, but so is going prepared. The balance is up to you. Absolute musts for me: emergency water purification tablets, tiny flashlight, paper map (I photocopied the pertinent part of a good-quality topo map), and sun protection (such as sunscreen/hat/sunglasses/SPF lip balm). Also recommended: Band-Aids and a bit of duct tape (for blisters and various other uses), a signaling device of some sort (my pack has a whistle, but mirrors and GPS emergency beacons are other options), weather-appropriate clothes and basic survival gear if you need to spend the night (I took a light-weight emergency blanket, which can also double as a signaling device or a sun shade), small pocket knife, basic emergency medicine (like ibuprofen and antihistamines), extra socks, hiking poles, and a bandana you can wet in the creek to help against the head (and which doubles as a scarf in the morning if it's cold).
6) Know where the water is and whether it's turned on at the moment (ask the day before at the backcountry office.)
7) Carry plenty of food (twice what you'd eat in a normal 12-hour period, including lots of salty snacks and carbs)
8) Carry plenty of water (I advise 3-4 liters, which you refill every chance you get. If for some reason there's no water at Indian Garden or the River, or if temperatures are flirting with 100 in the Inner Canyon, you'll have to take more or not attempt the hike. If there's water at 3-Mile Rest House and 1 1/2-Mile Rest House, you might be fine with 2 liters, but that's not giving you a lot of leeway if anything goes wrong).
9) Take and use electrolyte drink mix (I like Pedialyte. Other friends suggest Liquid IV or Vitalyte). When it's hottest and hardest, alternate plain water and electrolytes in a 1:1 ratio.
10) Start EARLY. We're talking dawn...or earlier (though it will depend somewhat on the season)
11) Have someone up top or at home who knows your plan and will get help if you don't show up or make contact. As always, it's safer to hike with a partner, but if you're prepared and want to solo it, there are enough other people on the trail that you won't really be alone.
12) Have fun!