*****Great book!!!! The PDF is bookmarked and has links to jump back and forth when they refer to other rules for quick reference. I especially like the rules for setting up camp, tracking food and resting in harsh environments. IMO the rules could be used for overland travel too just depending on the location of the PC's. The rule for tracking food is simple and I really like how the players can choose to burn HD to go farther and farther into the unknown depths all while risking there lives. This is a great supplement for 5e but works great for all systems and the other great part is you can use what u want and throw out the rest. This deferentially streamlines what to do when they want to rest and short rest in harsh environments. I have not looked over the old version by TSR but I will I haven't had time yet. What I like also is these rules add grit to the game PC's aren't jus gonna travel forever with out going back to civilization or using their resources with care. I like that the ppl that wrote the book play FRPG's a lot so they know what works and what doesn't after countless hrs of playing I'm sure. For a current updated resource for traveling long distances over harsh environments look no further this book should be ur first choice. I give it 5 stars!!

Update 5/12/2022 I had time to look over the old TSR guide and as I did find it useful I like Survivalist's Guide to Spelunking better as I play a lot of 5e. The mapping section in Survivalist's Guide to Spelunking I can see myself using compared to the older method presented in the TSR book. This book out the gate needs no adjustments for 5e, I like that. Every time I look over the PDF or pick up the book I find something new to read about the game. I especially like the chapter on light and sources of light underground. I like the idea of the rest pently as I like to run a grittier game. Streamed lined rules for finding and setting up camp. If ur looking for rules for an underground campaign this is ur book. I wish I had this book when I ran my underdark campign it would of helped me without a doubt. Great PDF super fast to navigate. Crytal depths ahead my friend.