user38618: I heard that there was an old block with one transaction and it takes 20 seconds of CPU time to verify.
1) Which block was it? I forgot its block height.
2) Is there a block that takes more time to verify? Or is there a similar block?

user30668: I'm not completely sure if this is what you are looking for, but it may be.
Here you have a type of transaction that takes 3 minutes to verify, and that was reported back in 2013. (CVE-2013-2292). Moreover, in Sergio Demian Lener's blog you can find a related topic, where he explains how he found a vulnerability that used the FindAndDelete function and OP_CODESEPARATOR to create a transaction that toke up more than 5 hours to verify.

user48884: bb41a757f405890fb0f5856228e23b715702d714d59bf2b1feb70d8b2b4e3e08 is usually the transaction referred to as being the megatransaction that took seconds to verify. It is the only non-coinbase transaction in block 000000000000000003dd2fdbb484d6d9c349d644d8bbb3cbfa5e67f639a465fe.
Nowadays this transaction is verified much faster than 20 seconds. Last time I benchmarked this, it was ~1 second. With the introduction of assumevalid in Bitcoin Core 0.14, the transaction's signatures are no longer fully validated so it takes the same time as most other blocks, ~60 milliseconds.

38618: <p>I heard that there was an old block with one transaction and it takes 20 seconds of CPU time to verify.</p>

<p>1) Which block was it? I forgot its block height.</p>

<p>2) Is there a block that takes more time to verify? Or is there a similar block?</p>
 30668: <p>I'm not completely sure if this is what you are looking for, but it may be.</p>

<p>Here you have a type of transaction that takes 3 minutes to verify, and that was reported back in 2013. (<a href="https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2013-2292" rel="nofollow noreferrer">CVE-2013-2292</a>). Moreover, in <a href="https://bitslog.wordpress.com/2017/01/08/a-bitcoin-transaction-that-takes-5-hours-to-verify/" rel="nofollow noreferrer">Sergio Demian Lener's blog</a> you can find a related topic, where he explains how he found a vulnerability that used the <code>FindAndDelete</code> function and <code>OP_CODESEPARATOR</code> to create a transaction that toke up more than 5 hours to verify.</p>
 48884: <p><a href="https://blockchain.info/tx/bb41a757f405890fb0f5856228e23b715702d714d59bf2b1feb70d8b2b4e3e08" rel="nofollow noreferrer">bb41a757f405890fb0f5856228e23b715702d714d59bf2b1feb70d8b2b4e3e08</a> is usually the transaction referred to as being the megatransaction that took seconds to verify. It is the only non-coinbase transaction in block <a href="https://blockchain.info/block/000000000000000003dd2fdbb484d6d9c349d644d8bbb3cbfa5e67f639a465fe" rel="nofollow noreferrer">000000000000000003dd2fdbb484d6d9c349d644d8bbb3cbfa5e67f639a465fe</a>.</p>

<p>Nowadays this transaction is verified much faster than 20 seconds. Last time I benchmarked this, it was ~1 second. With the introduction of <code>assumevalid</code> in Bitcoin Core 0.14, the transaction's signatures are no longer fully validated so it takes the same time as most other blocks, ~60 milliseconds.</p>
