The paintings should be separated into 17 groups of three. Each group of three will contain one painting from the circle group, one from the square group, and one from the triangle group.

Each painting in a triplet will have something in common with the other two paintings, either style, subject matter or artist.

Each painting is numbered. Sum the three numbers, then find the letter represented by the sum (modulo 26 = keep subtracting 26 from the sum until you have a number between 1 and 26). Substitute A for 1, B for 2, ... Y for 25 and Z for 26.

When you are done, arrange the letters in order by the sum of the original three numbers, starting with the lowest sum, and going to the highest.

Grouping	Square	Triangle	Circle	Sum	Mod (26)	Letter
Religious	13	1	2	16	16	P
Picasso	6	11	4	21	21	U
Art Deco	19	9	10	38	12	L
Van Gogh	36	3	20	59	7	G
Surrealist	52	5	22	79	1	A
Children's Illustrations	45	29	23	97	19	S
O'Keefe	65	12	24	101	23	W
Rembrandt	48	18	39	105	1	A
Harlem Renaissance	57	37	30	124	20	T
German Renaissance	104	14	17	135	5	E
Renaissance	82	28	38	148	18	R
Art Nouveau	114	15	21	150	20	T
Neo-Classical	120	7	34	161	5	E
Pop Art	111	26	32	169	13	M
Landscapes	133	31	8	172	16	P
Futurism	145	16	33	194	12	L
Romantic	161	27	25	213	5	E

The answer spells

PULGAS WATER TEMPLE

Clue 13