|White to move and win|
I blitzed through the test, spending about 5-15 seconds per problem and the estimate of my Elo rating is 1998 (with a point spread from 1868 to 2128 which seems a tad big). As for the accuracy of the rating, who knows? I have not played tournament chess for nigh on to 40 years and my last pre-engine postal rating was around 2050.
The site also allows you to test your endgame knowledge. In this test of 24 positions you are simply asked to judge whether white can force a win. Afterward, you are given feedback on your answers. Again, I just gave answers off the top of my head and got half of them correct. It seems that, probably thanks to a cookie, once you take the test you can't take it again.
Anyway, one position on the endgame test that I found intriguing was from the Ruy Lopez Exchange Variation.
Can white force a win? My response was no. I know the ending favors white, but with only Kings on the board I did not think it was possible for white to FORCE the win. My thought was that for white to win the ending he would need at least one additional piece in order to take advantage of (or create) a second weakness in black's position. I was totally wrong!
White CAN win by force. The site's explanation is white wins because his superior P-structure allows him to create a passed pawn on the K-side. Their solution runs 1.Ke2 Ke7 2.Ke3 Ke6 3.f4 f6 4.Kd4 g6 5.g4 h6 6.h4 Kd6 7.e5+ fxe5+ 8.fxe5+ Ke6 9.b4. I am not sure how accurate this solution is though or what the source is, but in a Shootout at 17-25 plies Stockfish scored +5 -0 =0.
After checking a couple of sources I found Max Euwe gave the pure pawn ending (without pieces) as a win for white, and that the winning procedure is detailed in Secrets of Pawn Endings by Karsten Muller and Frank Lamprecht, but I don't have the book.
The Exeter Chess Club has excellent material on this ending and you can also go to Chessvideos and play this position against Crafty. Or, as an alternative you, could set it up against Stockfish on your GUI and practice trying to win it...good luck!
Just messing around with this Ruy Lopez position was both fun and frustrating, but if you are seriously interested in actually studying chess and maybe even learning something, this type of practice could be very useful...playing out positions from your openings or practicing various endgames.