wwall: Best seems 18.Nd3 Rb5 19.Nxb4 Rxb4 20.Rf1
Perhaps best is 19.d3 Ng3 20.Rg1 (or 20.Rh3 Re1+ 21.Kc2 Ne2 22.Nxe2 Rxe2 23.Kb3) Rd4 21.a3 Bd6 22.Bd2.
Better is 20.Kb3 Bxd2 21.Bxd2 Rxd2 22.Rab1.
not 21.Rxc1 Rxd2+ 22.Ke1 Rc2+ 23.Kc1?? Ne3 mate.
23.Rae1 Rd2+ 24.Kb3 Nd4+ 25.Kc3 Ne2+ 26.Kb3 Be5 27.Rhf1 Rxb2+ 28.Ka3 b5 29.Rxf7 b4+ 30.Ka4 Bg3 31.Rh1 Nc3+ 32.Ka5 Bf2 should win.
24.Kb1 Rd2 25.a4 (25.Rg1?? Nc4 26.Kc1 Rf2+ 27.Kd1 Nxb2+ 28.Ke1 Nd3+ 29.Kd1 Rd2 mate) Nxg4
26.Kb4?? Bd6+ 27.Ka4 Nc4 28.Kb5 (28.Rac1 Nxb2 29.Kb5 a6+ 30.Ka5 Ra3 mate; 28.Rab1 a6 and 29...b5 mate) Nxb2 29.Rac1 a6 30.Ka5 Ra3 mate.
Stronger may be 26...Nc4 27.b3 Nb6+ 28.Ka3 Bxa1.
Stronger may be 27...Ra3+ 28.Kb4 a5+ 29.Kc5 Rd3 30.Rhd1 Bd4+ 31.Kb5 c6+ 32.Ka4 b5+.
After 28...Rd4, Black threatens mate with 29...Nd2+ 30.Kc5 b6+ 31.Kb5 Kb7 and 32...a6 mate.
29.Kb3 Nd2+ 30.Kxb2 Rb4+ (or 30...Nxb1) 31.Kc2 Nxb1 32.Rxb1 Rxb1 (or 32...Rxg4) 33.Kxb1 Kd7 34.Kc2 b5 should win.
Or 34...Nh2 35.Kf6 Nf3 36.Kxf6 Nxh4.
36.Kf4 Kd5 37.Ke3 c5 38.Kd3 b5 wins.
Or 36...c5 37.Kg4 Kd5 38.Kf3 Kd4 39.Ke2 Kc3, winning.