I am more inclined to interpreter 厚重沉实 as a description of the wooden pillars in the 四合院. And the author imagined that heaviness of the pillars (what he saw) was transferred to his “heavy/steady/slow" steps (what he felt).
厚: 豐厚 "thick; rich (in history)"
重: 貴重 "weighty; of great (historical, cultural, artistic) value"
沉: 沉穩 "stable due to low center of gravity; anchored, able to hold in place" (韌度高的木材加上卯榫結構使四合院堅穩耐震)
實: 實在 "real; solid" (四合院用原木, 真材實料; 工藝精確扎實, 設計古樸實用)