There are not a lot of rules similarities between Pathfinder Second Edition and Dungeons and Dragons 5th Edition, but I've recently noticed one very significant similarity when designing adventures for each system.

They both usually handle sandbox adventures very well--with certain limits.

I've talked about sandbox adventures before; they're the kind of adventures where the heroes can go anywhere they want in a large area and follow up on whichever leads strike their fancy. It's a lot of choice about what to do, like playing in a sandbox. (My previous blogs talk about how best to build them, and how some sandbox adventures might limit choice to provide an illusion of sandboxiness.)

It's easy enough to write a sandbox adventure that spans a single level. No matter where the heroes go, they're still 6th level (for example), so 6th level challenges are appropriate for them anywhere. But what if you want a bigger sandbox? What if you want one that spans two or even three levels, with a ton of choices?

Multi-level sandbox adventures are hard in some game systems where difficulty is keyed pretty tightly to party level, so you need a lot of tricks. You don't need a lot of tricks, however, in Pathfinder Second Edition or D&D 5E. Here's why:

Pathfinder Second Edition: XP Scales For You. The structure of XP in Pathfinder Second Edition means that a party that faces challenges higher than their current level earns more XP, and a party that faces challenges lower than their current level earns fewer XP. For example, an encounter listed as "Low 8" is the same as "Moderate 7," so 7th-level characters earn 80 XP for it, not 60 XP. But although they might reach 8th level quickly with these higher awards, a "Low 7" encounter is equivalent to "Trivial 8," giving them only 40 XP rather than 60 XP. They'll naturally slow down, and their progression will stay mostly the same. This means you don't have to think too much about how to scale your sandbox challenges; put half of them at the lower level and half at the higher level and everything will work out fine.

D&D 5E: Bounded Accuracy. The limits on what monsters and players can do in D&D is intentionally limited by the system to make unhittable defenses or impossible skills all but impossible for characters near the intended level. This is a design philosophy, not a formal rule, but the fact that so many difficult numbers are static regardless of player level, and that player numerical increases are much more flat (proficiency modifiers only go up from +2 at 1st level to +6 at 20th level). This means that a sandbox adventure that spans multiple levels is very often totally fine.

So what levels are good for multi-level sandbox adventures? Nearly all of them. But keep these three rules in mind:

* Don't do it across the lowest levels. Characters generally get a pretty big boost in power between 1st level and 2nd level, so encounters keyed for a 2nd level party can be pretty overwhelming at 1st level. D&D 5E gives a really big class choice (and boost in power) at 3rd level as well, so a 3rd level party can much more easily handle 2nd-level threats. It's therefore often best to avoid multi-level sandbox adventures for starting characters without some guide rails (like letting them easily flee).

* Don't do it across ability score increases. Pathfinder Second Edition gives pretty big increases in power when the heroes get their ability score boosts (like at 5th level). The difference between a 5th level party and a 4th level party is much bigger than the difference between a 6th level party and a 5th level party. In Pathfinder Second Edition, don't have level 4-5, level 9-10, or level 14-15 multilevel sandboxes. Ability score increases in D&D 5E don't give as big a boost, but characters gain some other measurable increases in power at about the same time they get their ability score boosts.

* Don't break across "tiers." Tiers of play are a nebulous concept, but they break the character levels up into narrative bands. Low-level heroes handle local troubles; mid-level heroes handle nation-wide troubles, and high-level heroes handle planes-wide threats. D&D 5E expressly defines these as follows: 1-4, 5-10, 11-16, and 17-20. They're less specific in Pathfinder Second Edition and other games, but usually hit the same benchmarks for reasons of character abilities. At 5th level, heroes can finally fly, make large area attacks, and gain significant improvements in their weapon abilities (gaining critical hit effects and so on). At 9th level, characters can more easily and permanently affect their environment, come back from the dead, and visit other planes. If you want your multi-level adventure to have narrative consistency, it shouldn't break across these tiers of play.  

Have fun building the sandbox!