60th birthday present ideas?

My father’s birthday is coming up in, like, um, tomorrow. I knew that. What I’d forgotten is that it’s his 60th. I think I need to think of a better present than I have now (so lame I won’t even mention it), and do it quickly. Any suggestions? I know, I know him better than you guys do, but he’s difficult to shop for - he’s a math professor and does a lot of writing on that topic, but that’s about it. No other major hobbies and interests. Computers and electronics are pretty much out - he just bought a new laptop and that seems to fill all his needs. He hasn’t used the PDA I gave him before. My budget is a couple hundred dollars, maybe up to $400 or so if it’s worth it.

I realize it would be best if I could take him somewhere or do something with him, but I really have no free days for the next month or so.

Perhaps a professional massage? Or a series of them? If he sits a lot, it might do him some good. Or a raincheck to do stuff or eat out a month or so from now when you get free time.

Some random ideas

a hot air balloon ride

a plane ticket to visit you

ballroom dancing lessons–if he lacks a partner (like your mom divorced him years ago or something) that’s not really a hindrance. A single man in a ballroom dancing class will always have a partner, believe me.

a massaging chair (I think these are usually more than $400, but maybe not?)

A really nice pen - I know it sounds lame, but some of the newer pens are pieces of art (with prices that can sometimes match pieces of art). I’m thinking mahagony or stone finish, large - either fountain pen or rollerball.
It is a quiet gift, but is personal and something no one wants to go out and buy for themselves.