A non-sandbox sandbox campaign.
In D&D terms
create seven adventures #1-#7 set to level 1 to level 7 adventures
1) adventures #1-#6 each have two paths:
– the main path set at the specified level
– a path set at the player’s current level leading to a random clue to an adventure #1-#6 they haven’t received yet.
2) the 6 secondary paths would be like mini-adventures or single encounters
2) completing adventure #1-#6 gains 1/6 of a clue to adventure #7
3) whatever direction the players go in at the start they hit a level 1 encounter containing a random clue to adventure #1-6
Level 1 party go east (or any other direction) and encounter something that drops a clue.
GM rolls a 3 so the player get the clue to adventure #3
Fork in the path in adventure #3, main path is level 3 and the players will probably get stomped if they try. secondary path will be the level 1 mini-adventure because the players are currently level 1
assume players run from main path but succeed at secondary path gaining second clue
GM rolls and get a 3 again so re-rolls and gets 5 so players get clue to adventure #5
players get butt kicked again on the main path but the secondary path – using the level 2 secondary path now the players are level 2 – gains them a 3rd clue and it’s a 1
now level 2-3 the players attempt the level 1 adventure and win gaining the first part of the clue to #7. the level 3 secondary path gains them the 4th clue which rolls out randomly to adventure #4
It doesn’t have to be level. In Cthulhu terms you’d just have a bunch of adventures, a randomized first clue and other hook clues in spots in each adventure that could be discovered by beginning characters and and make sure the players understand that running away is a perfectly good option.
The players might stumble on to things that are too big for them early on but if in the process of investigating followed by running away they gain a few skill points each time then gradually tough adventures become less tough e.g. one adventure might have a bottle-neck where the players need 50% Mythos knowledge but they could complete the first third of the adventure and that might contain a hook to another adventure.