Yet another idea... :\

Honestly, to define the idea of a sandbox game, a sandbox game doesn't have an end. The draw there is that a person continues to play and sees their progress as they continue forward. That's why people play Minecraft: not to try to beat the ender dragon on the hardest mode, but instead to try to see how cool of a creation they can make, to see how advanced they can get in their crafting knowledge, to alter the world around them, or to see what kinds of cool locations they can discover. It's the feeling of progress that brings people to play it, not just the smaller parts that people enjoy.

The Kobold guide to game design (a very good book) teaches that if you want to find out why a game is successful, analyze what feeling it evokes in the players and therein will lie its success. For this genre, players of minecraft, and other sandbox games, enjoy them because they let the players feel in control, and like the choices that they make matter.

The trick with board games is the lack of components that can fit into the box, and how much time players are willing to devote to a paticular board game. If you've really made a lot of progress, it's going to be hard to set up the game to a previous setting (like a saved game) because so many parts would have to be different as a result from the original base setup. This is probably why many board games don't have sandbox elements: you can't have an eternal game unless a) you can save and continue the game later, or b) you have infinite time to play games.

However, in a sense, TCGs have this sandbox flavor about them because players amass cards and can continually improve their decks and watch as they improve over others. They also gain enjoyment from seeing their ideas be successful as implemented in decks. They gain progress and rewards for continuing to play. In a sense, the metagame of that game can allow it to be continually played forever, without having to reset components.

Another easy way to do this is to have no components: a good Game Master in any RPG should make the game have this sandbox feel with the storytelling and with the character development. Players should be allowed to enjoy the wealth and powers they've accumulated, and see just how easy it is to beat an enemy which 5 levels before had scared the daylights out of them.

In another sense, Risk Legacy did this very well with having a game be simple to set up every time, but you have indicators that show progress and remind you of previous victories. If a player won, they get to permanently change the game, and the overall game after a few rounds is different every time you play. Their victories and choices matter, and the players feel like play matters more.

So anyways... my point is that sandboxes are hard to do as board games. Legacy mechanics, collection games and RPGs are really the only ones that can offer true sandbox elements.

...

I just realized that I wrote a post entirely irrelevant to the second part of your question.

...

However, if you're going to just the idea of building, crafting, and interactable terrain, there are lots of games out there that meet those criteria. I am currently working on a risk-esque game where the players can build starbases that shut down the jumping between planets (which are essentially continents). This changes the game significantly. Interacting with terrain is one of my favorite elements to try to include.

Also, check out the Game Design Showdown on this site: sometimes you'll get ideas from looking at older entries that might push you on the right path.