is the biggest and the most time consuming virtual environment I have made. The fantasy Island was created with 340 static meshes and almost 200 textures that are used in 85 materials... It took me 6 months to go from first sketches to final enviornment. The whole thing is for sale on UE 4 marketplace: https://www.unrealengine.com/marketplace/en-US/slug/gothic-island as a pack. There will also be a version for Unity, which I am currently working on.
During developement of the pack I changed a theme and idea completly. At first the map was supposed to be called "Gothic Caves" and everything would be hidden inside a mountain. I planned on making complex maze of corridors and larger halls with flying buttresses and Gothic vaulting - all inside caves. HOWEVER after a game called Apex (battle royale) came out I decided to scratch the original idea and make environment which is large and royale-like. I started making enterable building meshes, city battlements, landscape elements....
When developing an environment it is very important to keep on sketching new ideas, asking people about their opinions, judging your scene from different perspectives and trying new things. There are moments of doubt (which is normal) usually caused by wrong distribution of the designer's attention. Designers MUST pay attention to entire level! They can't just focus on one small part of the map, neglecting the rest! Making a small part of a map in disregard of the rest leads to all kind of problems: inconsistancy, lack of "flow", poor gameplay and eventually irritation or even burn-out of a designer. Players will explore. The most important is their experience of the whole creation. Don't worry too much about small corner behind that rock...if there is bug/glitch/mistake - players will surely find it. Despite that they are much more forgiving if the whole picture is right.