Hi

Im doing a fantasy turn-based tactical rpg/management game where you control a group of heroes (up to 6) that travels, explores dungeons, gather resources and visits towns.

You set out on the journey and choose your next step (can be a dungeon or a general location such as forest or highland). Each step brings you closer to your final goal = the "last dungeon". Clearing this dungeon will "win the campaign".

Similar games such as darkest dungeon and in a sense also battle brothers (fights and management part) has a "limitless grinding" to it. You simply can repeat easy missions infinitly to level up and find more equipment. I'd like to avoid this.

There is two "world states" in the game: time and distance. Each day has 3 phases and then you rest (and heal). Depending on your route you travel different distances each phase (in leagues) or stay on the same location (to hunt or mine for example). Once you reach the end (x leagues away from the start) the final dungeon is reached and you must face it.

My idea is to have the world become harder each day, so a player can not linger and just amass xp and loot. So you have an incentive to travel on. Is this good? What other design could I make? It also makes sense that the world gets harder when you get closer to the end.

Another idea is to have towns show up only each x leagues, and you need towns to resupply. That would force the players party forward.

I want the player to be able to make a choice: do I stay in this location and explore (for loot and other resources) or travel on. How to achieve this?

In a game like diablo you never make any choice. If you progress to quickly you will just slow down your journey until your level reaches what is suitable for that area. Not so fun.

The entire point of grinding as an RPG mechanic is as a means for the player to control the effective difficulty of the game by building up experience and/or equipment to the point where the player feels ready to take on the next challenge.

Thus, you should be very careful when designing systems in RPGs to discourage or punish grinding. The most common method of doing this is via exponential XP curves and item prices - the player can, at any point, grind as high as they want, but beyond a certain point, it becomes extremely inefficient to do so. The last thing you want to have happen is for the grind-difficulty relationship to flip, such that the game becomes harder and harder as you grind more - this means that the player who wants a more challenging game is the one forced to grind for it. This is bad for two reasons: first, the player who wants a challenge is forced to play more and more unchallenging content as their skill improves; and second, the player who feels unready to advance in the game is left with no recourse beyond just starting over.

If you absolutely insist on discouraging grinding, just don't even make it an option.

I believe grinding is the "easy" way to add length and smooth out the curve in progression-based games. In aRPGs like Diablo, without the grind, you'd reach the maximum too fast, eliminating the replayability it is known for. On the other hand, if you are always progressing (due to lack of grinding), your improvements are likely meaningless, at least in the immediate sense.

I'd say Slay the Spire reached a good balance and studying that game might give you a nice starting point to build your game (and this analysis of the progression is quite interesting to read also https://www.rockpapershotgun.com/2018/07/05/what-works-and-why-juicy-maths-in-slay-the-spire/).

Going a bit back in time, you could have something similar to Jagged Alliance, that is, a map where you can travel at your pace, then you'd add more and more perils the longer you linger (like being chased, or something, making you always on the move, gently pushing you towards the end area). 

Hmm so maybe something like this:

The player can stay in a region, explore it, find towns there, find dungeons there etc. But the general difficulty stays the same. 

You can stay in a region as long as you want. You still pay resources like food and supplies for your heroes and after a while you do not gain so much new useable stuff in the region.

When the player feel the party is strong enough the player can opt to "travel east with the caravan in town" or something, which brings the heroes to a harder region (but you can never go back, because you are such brave champions!).

The fifth and final region contains the final dungeon which is unlocked by doing some things in the final region (like find key, perform ritual whatever). This would be similar to how bosses are unlocked in darkest dungeon.

I'd personally also nudge the player forward to avoid the sense of 'must explore everything before going' and being more like 'I'll try this differently next time'. Perhaps healing supplies dwindle, or there's more enemies around. Another possibility is to add a type of bonus if you reach a region before a given time.

Avoiding grinding is easy:

1. Don't reward the player for repetitive actions.
2. Don't make the player dependent on the rewards from repetitive actions in order to advance.

The simplest way to avoid grinding is to imply not put any repetitive actions in the game.  Place a finite number of enemies and treasures in the game, and don't ever respawn them.  Or do respawn enemies, but don't give any rewards for defeating them.

Generally speaking, grinding isn't something that finds its way into games by accident.  It's something that's deliberately placed in a game to create a 40 hour game from 1 hour of content.  You avoid that by either creating enough content for the full length of the game, or by reducing the length of the game to match the content.

By the way, coincidentally, a while back I was thinking about a rather similar game (in the sense of a caravan traveling towards a goal, turn-based combat). since I'm unlikely to work on this idea any time soon, I'll write what I had coarsely in my mind in the hope that it might be useful to you.

The main idea would be to have a caravan journeying towards a goal (the reason could be anything, really). Actions would run in accelerated real time. Action would include traveling, foraging for resources, healing, fixing equipment, scouting the region and so on. Time taken to complete each of those and degree of success would be based on skills of the characters doing those things. In principle, there would be no limit to members of the caravan, but find food and camping supplies to many people would make large caravans impossible. The journey would be dangerous, and staying long in one place wouldn't be wise, as the perils of the land would close in the caravan. Part of the challenge would be to manage the different aspects of the caravan, making it efficient in terms of combat and survivability. On top of this, elements of RPG would be added, mainly in the villages and ruins found along the way. Another point is that the 'active group' would be limited, as the other would be taking care of the caravan (say, while other go explore some ruins). All in all, it would play a bit like Expeditions and Thea: Awakening, but with more emphasis on what happen in the caravan and its members.