

I can also recommend a few vehicle add-ons: Visually, the most impressive maps I've seen for this game were those made by Fishke – RP_SouthSide and its slightly smaller predecessor, RP_UnionCity (as well as their day versions) – these are great fun, especially with vehicles. It has city bits, countryside bits and even a working train (which teleports you to another area of the map when riding in it). Rp_NewExton2 is a HUGE map set in Australia, with many roads.

I can also recommend the map gm_susquehanna, it's a really well made US suburbia-type map, set in Pennsylvania. The creator of this map also made another huge map with snowy mountains (and a large multitude of underground areas) called gm_boreas. The map is huge, and features a castle, mountain roads, an air strip, a sizeable town and (quite prominently) the coast. This is actually the first map I've tried after the base game maps (back in late 2016), and it's a really good one. It also features quite few underground areas. If you're looking for huge open map with a lot of space to build things on (basically a mega-sized version of gm_construct combined with gm_flatgrass), I can recommend gm_genesis.

NOTE: The Steam Workshop features many maps that use assets from other games and thus require the user to own (and mount) these other games in order to work properly, but none of the maps I've listed below require any other games. Most of the below maps I've suggested were made for driving around on them with vehicles, but they can also be used for other things too (such as building your own contraptions and trying them out). I of course don't know what kind of gameplay your son enjoys, but here is a list of addons that I have found very enjoyable.
