In the Olden Days

Prior to the wretched 3rd edition of Dungeons and Dragons, and everything that came after that, foul spawn of goat's arse that it is, the hit points stopped flowing like cheap wine at level 9.  Level 9 was the last time you rolled a hit die for your character's hit points.  From 10 to 20 (or whatever the end level was) your character received a set amount of hit points based on class and no more constitution bonuses.  Sounds unfair to the modern audience but it was very logical at the time.  Level 10 started what you might call the endgame content of the tabletop experience.  Players had the option of building strongholds, the type determined by their class, and becoming a part of the world, vice the itinerant housebreakers they had been up to that point.
Wizards might want to do spell research to invent new spells.  In order to do that they would need a fully stocked library and laboratory.  This was not the MMO bollocks of popping into some handy public crafting hall with an alchemy table and spending some 10 minutes to work up a recipe.  This was full on, creepy, stuffed lizard hanging from roof, calling up extra-planer forces for a chat about the nature of elemental painfiredeath spells.  To make this happen a wizard needs to build a tower.  It was very much a part of the OD&D game and still around as late as 2nd edition.
Fighters built keeps, Clerics built temples, thieves built guildhalls and rangers...well rangers just ponced off to the woods and built a tree-house or something.  Rangers don't build keeps.

This might seem odd to a modern gamer.  One of the many problems I have with 3rd edition onward is the attitude that the players just keep getting better at a set rate.  There is no diminishing returns.  Pathfinder, which I loathe immensely, even felt that the little darlings were getting butthurt feelings from having "empty levels", that is, levels that gave them no special pretty new abilities to go with the extra hit points, skill points, and possibly increased combat bonuses.  Well couldn't have that, could we?  Nope.  Pathfinder gives you a cookie every level, maybe two or three cookies.  And best of all you never stop getting better.  That's right, it's just bonus after bonus after bonus.  Of course the monsters had to be upgraded too, so really it's bloody stasis, innit?  You fight kobolds at first level then you graduate to goblins then orcs and so on.  The monsters will always be just right for your skills and powers.  Sissies.
Meanwhile you are thinking you are going to be bloody Aragorn, but then Aragorn settled down and became king of Gondor.  Not you though, just a life of taverns, sleeping in inns, meeting scores of easily replaceable NPCs and fighting monsters for gold.  Where the hell are you putting all that gold?
I want to know, dammit!

Investments.  You should be taking that gold and building a keep.  Land economy, that's the key to pseudo-medieval fantasy.  Get some land, build a keep.  Now you can keep loads of gold and jewels in your keep, guarded by your men-at-arms and wait for some other itinerant housebreakers to come along then you can kill them and take the stuff they've been looting from dragon hordes all over the land.  Building a keep is the logical adult growth of your character.  You will have a home-base for storing your magic items and a place to rest and recuperate after an adventure that won't involve trying to get an innkeeper to make change for a platinum piece.  You can have in-depth adventures where you are invested in the world itself.  Political intrigue, if you like, but not necessarily.  Killing the necromancer that is terrorizing a village is all very heroic and good, and we thank you for doing it, but how about defending the village that has sprung up on your land?  The very people you are supposed to be defending, since they pay rents and all.

 "But we don't want to break up the band," you say.  Fair enough.  The rules don't say that your party has to build separate keeps, you know.  How about a huge keep complex with a temple, a main castle, a wizard's tower and a small town on the land (where the thieves' guild is located)?
You could effectively run your own town that might one day grow into a city.  It's like playing Sim City and D&D at the same time!
This is what we call endgame.  MMOs all have this problem.  You've leveled your character to the highest tier possible and now what do you do?  The game developers want you to keep playing, keep paying that subscription fee, and thus making them money.  They have to give you something so they push out new content, new events, and generally keep you hanging on.  If they have some sort of war as well, say Horde versus Alliance or the three-way Realm War of Dark Age of Camelot you can feel invested in continuing the game after the simple Pavlovian level cookie grind is over.  Your tabletop experience also has an endgame.  You just have no more leveling to do.  Oh, it's gotten boring now.  You miss the sweet levels between 4 and 15 when monsters were still a threat but you had a chance of survival past one fight with some surly goblins.  Pre-3rd edition this was marked by level 9.  From here on out you'd still get a few hit points, still earn spells, your combat profile would still improve but you weren't getting as good as fast as you had been.  Monsters would still be a threat for the rest of your character's life.  If you were playing AD&D age would eventually lower your stats as well.  Time to consider a new lifestyle, not retirement, but definitely one where your character had more to do than ignore the encumbrance rules so he could carry around 900,000 pounds of coins.

"We're not playing ledgers and accountants, we are playing a game of adventure."

Well maybe you should be.  Look at the books and films that are adventure and see how adventure comes from adversity.  What is the point of a light spell if all dungeons are magically lit by ever-burning torches?  What is the point of the long trek through the wilderness with a competent guide, like a ranger, if nobody need worry about starvation and the elements?  Where, essentially, is the adventure and WHERE IN THE HELL ARE YOU KEEPING ALL THAT GOLD, DAMMIT?
This is why the original game, and following editions, had the rules that it did.  Most gamers play like they are pirates, scoring some gold and then wasting the bulk of it on overpriced stays in inns, drinking bouts, and shiny baubles that they fritter away and then it's back to sea again to score some more gold.  Or in this case another dungeon.  Let's face it, if a town sees a group of racially mixed, heavily armed, and obviously not working class people coming they should immediately jack up the prices at least 500%.  It's like having a carrier pull into port.  The locals know that money is a-comin' and they will fleece the party for every scrap of copper they can get.  Normal price for a pint?  A ha'penny. During Adventurer Week? 2 silvers.  See what I mean?

For this reason all new games can toss a rainbow colored, cotton-candy flavored clown salad.  Diminishing returns, endgame, build a keep.  A whole new world of gaming awaits you.