We've gone to the spa, to the casino/race track, snowboarding, horse-back riding, mini-golfing, and just driving along a beautiful view...
For splurges, we took sailing lessons together, rented a boat and packed a basket for a romantic picnic on the lake, spent a night at a quaint bed & breakfast...
We talk about playing a round of "real" golf together, going to a wine or bourbon tasting, and trying to get a group together for a dinner club (cooking is fun for both of us), but all of those things will wait until we're through this pregnancy...
My brother and sister-in-law like to sneak away to the family cabin in the woods and they did an adults-only bible group together...
Some of these may be less spontaneous than you'd like, but hopefully they give you some ideas about things that will be more special to the two of you :)