Part of the infield gallery seats on the top level...
You'll be super glad to see that there is only maybe 12 rows total in this section since most of the seats are focused on the lower level at Nationals Park. The stair cases aren't all that steep if you compare them to Oriole Park in Baltimore.
There will be plenty of railing up there to help guide you to your seats, though. Ticket prices for 312 set us back $40 for two seats. I didn't complain, we had fun and could follow what was going on rather easily. Plus, you can stretch out up there when the section isn't all that full. The ticket prices are reasonable especially since the team has been exciting to watch lately with the addition of Bryce Harper.

If you're visiting Washington DC and have time on your hands to take the actual ballpark tour, it's $15 for adults and is well worth the money.